Interesting Things to Know about MySQL Mike Chirico (mchirico@users.sourceforge.net) Copyright (c) 2004 (GNU Free Documentation License) Last Updated: Sun Jan 21 09:44:21 EST 2007 The latest version of this document can be found at: http://souptonuts.sourceforge.net/readme_mysql.htm TIP 1: Find out who is doing what, and kill the process if needed. This example kills Id 657. mysql> show processlist; show processlist; +-----+------+-----------+---------+---------+-------+-------+------------------+ | Id | User | Host | db | Command | Time | State | Info | +-----+------+-----------+---------+---------+-------+-------+------------------+ | 657 | prog | localhost | weather | Sleep | 28619 | | NULL | | 782 | prog | localhost | weather | Sleep | 853 | | NULL | | 785 | prog | localhost | NULL | Query | 0 | NULL | show processlist | +-----+------+-----------+---------+---------+-------+-------+------------------+ 3 rows in set (0.00 sec) mysql>kill 657 Or, from the command line, to kill process 782 [root@third-fl-71 mysql]# mysqladmin processlist +-----+------+-----------+---------+---------+------+-------+------------------+ | Id | User | Host | db | Command | Time | State | Info | +-----+------+-----------+---------+---------+------+-------+------------------+ | 782 | prog | localhost | weather | Sleep | 2676 | | | | 785 | prog | localhost | | Sleep | 1823 | | | | 793 | root | localhost | | Query | 0 | | show processlist | +-----+------+-----------+---------+---------+------+-------+------------------+ [root@third-fl-71 mysql]# [root@third-fl-71 mysql]# mysqladmin kill 782 Note, the following can also be helpful mysql> show status; or mysql> show status\G also mysql> show innodb status; or mysql> show table status like '%'; The above gives you create time and other information. TIP 2: Clean up binary log files. For a default install they may be in /usr/local/var/ or /var/lib/mysql/ with names ending in -bin.000001,-bin.000002,.. The following command may help find out where the logs are located. mysql> show variables like '%home%'; +---------------------------+-----------------+ | Variable_name | Value | +---------------------------+-----------------+ | bdb_home | /var/lib/mysql/ | | innodb_data_home_dir | | | innodb_log_group_home_dir | ./ | +---------------------------+-----------------+ mysql> reset master; reset master; Query OK, 0 rows affected (0.02 sec) See (Tip 24:) details working with binary log files and (Tip 25:) explains how to setup logging. (Tip 37:) shows have to setup MASTER and SLAVE replication. TIP 3: Can the order of the columns in a create statement make a difference? YES create table t ( a int, b int, timeUpdate timestamp, timeEnter timestamp ); The first timestamp will always be the "automatically generated" time. So if the record is updated, or inserted, this time gets changed. If the order is changed, "timeEnter" is before "timeUpdate", then, "timeEnter" would get updated. First timestamp column updates automatically. Note, in the table above timeEnter will only get updated if passed a null value. insert into t (a,b,timeEnter) values (1,2,NULL); Hints: Need mm-dd-yyyy hh:mm:ss format? select a,b,DATE_FORMAT(timeUpdate,'%m-%d-%Y %T'),DATE_FORMAT(timeEnter,'%m-%d-%Y %T') from t; +------+------+---------------------------------------+--------------------------------------+ | a | b | DATE_FORMAT(timeUpdate,'%m-%d-%Y %T') | DATE_FORMAT(timeEnter,'%m-%d-%Y %T') | +------+------+---------------------------------------+--------------------------------------+ | 3 | 2 | 04-15-2004 19:14:36 | 04-15-2004 19:15:07 | | 3 | 2 | 04-15-2004 19:14:39 | 04-15-2004 19:15:07 | | 5 | 5 | 00-00-0000 00:00:00 | 04-15-2004 19:15:53 | | 1 | 2 | 00-00-0000 00:00:00 | 04-15-2004 19:20:15 | +------+------+---------------------------------------+--------------------------------------+ 4 rows in set (0.00 sec) TIP 4: Connect, create table and select with Perl (Linux). First the DBI module is needed, which can be installed from the system prompt as follows: # perl -MCPAN -e shell cpan> install DBI cpan> install DBD::mysql The following is an example program: #! /usr/bin/perl -w # Copyright (GPL) Mike Chirico mchirico@users.sourceforge.net # # Program does the following: # o connects to mysql # o creates perlTest if it doesn't exist # o inserts records # o selects and displays records # # This program assumes DBI # # perl -MCPAN -e shell # cpan> install DBI # cpan> install DBD::mysql # # # # # use strict; use DBI; # You will need to change the following: # o database # o user # o password my $database="yourdatabase"; my $user="user1"; my $passwd="hidden"; my $count = 0; my $tblcreate= " CREATE TABLE IF NOT EXISTS perlTest ( pkey int(11) NOT NULL auto_increment, a int, b int, c int, timeEnter timestamp(14), PRIMARY KEY (pkey) ) "; my $insert= " insert into perlTest (a,b,c) values (1,2,3),(4,5,6),(7,8,9)"; my $select=" select a,b,c from perlTest "; my $dsn = "DBI:mysql:host=localhost;database=${database}"; my $dbh = DBI->connect ($dsn, $user, $passwd) or die "Cannot connect to server

"; my $s = $dbh->prepare($tblcreate); $s->execute(); $s = $dbh->prepare($insert); $s->execute(); $s = $dbh->prepare($select); $s->execute(); while(my @val = $s->fetchrow_array()) { print " $val[0] $val[1] $val[2]

"; ++$count; } $s->finish(); $dbh->disconnect ( ); exit (0); TIP 5: Remove duplicate entries. Assume the following table and data. CREATE TABLE IF NOT EXISTS dupTest ( pkey int(11) NOT NULL auto_increment, a int, b int, c int, timeEnter timestamp(14), PRIMARY KEY (pkey) ); insert into dupTest (a,b,c) values (1,2,3),(1,2,3), (1,5,4),(1,6,4); mysql> select * from dupTest; select * from dupTest; +------+------+------+------+---------------------+ | pkey | a | b | c | timeEnter | +------+------+------+------+---------------------+ | 1 | 1 | 2 | 3 | 2004-04-16 10:55:35 | | 2 | 1 | 2 | 3 | 2004-04-16 10:55:35 | | 3 | 1 | 5 | 4 | 2004-04-16 10:55:35 | | 4 | 1 | 6 | 4 | 2004-04-16 10:55:35 | +------+------+------+------+---------------------+ 4 rows in set (0.00 sec) mysql> Note, the first two rows contains duplicates in columns a and b. It contains other duplicates; but, leaves the other duplicates alone. mysql> ALTER IGNORE TABLE dupTest ADD UNIQUE INDEX(a,b); mysql> select * from dupTest; select * from dupTest; +------+------+------+------+---------------------+ | pkey | a | b | c | timeEnter | +------+------+------+------+---------------------+ | 1 | 1 | 2 | 3 | 2004-04-16 11:11:42 | | 3 | 1 | 5 | 4 | 2004-04-16 11:11:42 | | 4 | 1 | 6 | 4 | 2004-04-16 11:11:42 | +------+------+------+------+---------------------+ 3 rows in set (0.00 sec) TIP 6: Show status information on a table. Note, if the database was started with --safe-show-database or --skip-show-database some of these commands may not work. Note the "\G" option may provide a nicer format. Show the create statement: mysql> show create table dupTest\G show create table dupTest\G *************************** 1. row *************************** Table: dupTest Create Table: CREATE TABLE `dupTest` ( `pkey` int(11) NOT NULL auto_increment, `a` int(11) default NULL, `b` int(11) default NULL, `c` int(11) default NULL, `timeEnter` timestamp NOT NULL, PRIMARY KEY (`pkey`), UNIQUE KEY `a` (`a`,`b`) ) TYPE=MyISAM DEFAULT CHARSET=latin1 1 row in set (0.00 sec) TIP 7: Transactions: Not all table types support transactions. BDB and INNODB type do support transactions. Assuming the server has NOT been started with --skip-bdb or --skip-innodb the following should work: mysql> create table tran_test (a int, b int) type = InnoDB; mysql> begin; mysql> insert into tran_test (a,b) values (1,2); mysql> select * from tran_test; select * from tran_test; +------+------+ | a | b | +------+------+ | 1 | 2 | +------+------+ 1 row in set (0.00 sec) mysql> rollback; mysql> select * from tran_test; select * from tran_test; Empty set (0.00 sec) Summary: rollback undoes everything and commit will save. TIP 8: MERGE: Several tables can be merged into one. CREATE TABLE log_01 ( pkey int(11) NOT NULL auto_increment, a int, b varchar(12), timeEnter timestamp(14), PRIMARY KEY (pkey) ) type=MyISAM; CREATE TABLE log_02 ( pkey int(11) NOT NULL auto_increment, a int, b varchar(12), timeEnter timestamp(14), PRIMARY KEY (pkey) ) type=MyISAM; CREATE TABLE log_summary ( pkey int(11) NOT NULL auto_increment, a int, b varchar(12), timeEnter timestamp(14), PRIMARY KEY (pkey) ) type=MERGE UNION(log_01,log_02) INSERT_METHOD=LAST; mysql> insert into log_01 (a,b) values (1,'log1'); mysql> insert into log_02 (a,b) values (1,'log2'); mysql> select * from log_summary; select * from log_summary; +------+------+------+---------------------+ | pkey | a | b | timeEnter | +------+------+------+---------------------+ | 1 | 1 | log1 | 2004-04-16 11:59:55 | | 1 | 1 | log2 | 2004-04-16 12:00:08 | +------+------+------+---------------------+ 2 rows in set (0.00 sec) Reference: http://dev.mysql.com/doc/mysql/en/MERGE.html TIP 9: Updating foreign keys in a multiuser environment. Using LAST_INSERT_ID(). Also see (TIP 29) after reading this. The LAST_INSERT_ID() is unique to the login session. This allows updating of foreign keys. CREATE TABLE keytest ( pkey int(11) NOT NULL auto_increment, ptext text, ptype int(11), timeEnter timestamp(14), PRIMARY KEY (pkey) ); CREATE TABLE foreignkeytest ( pkey int(11) NOT NULL auto_increment, pkeykeytest int(11) NOT NULL, ptext text, ptype int(11), timeEnter timestamp(14), PRIMARY KEY (pkey) ); mysql> insert into keytest(ptext,ptype) values ('one',1); mysql> select LAST_INSERT_ID() from keytest; +------------------+ | last_insert_id() | +------------------+ | 1 | +------------------+ 1 row in set (0.03 sec) mysql> insert into foreignkeytest (ptext,pkeykeytest) values ('one',LAST_INSERT_ID()); Note: If your session didn't update any records, LAST_INSERT_ID() will be zero. Never assume LAST_INSERT_ID()+1 will be the next record. If another session inserts a record, this value may be taken. You are assured that this value will be unique to the "session". **SPECIAL NOTE: MySQL 4.1.2. supports UUID. mysql> select uuid(); +--------------------------------------+ | uuid() | +--------------------------------------+ | 167c1afe-0a0f-1027-891e-0004e222b485 | +--------------------------------------+ 1 row in set (0.00 sec) "A UUID is designed as a number that is globally unique in space and time. Two calls to UUID() are expected to generate two different values, even if these calls are performed on two separate computers that are not connected to each other." So in the future, UUID() could be used as a better primary key. The advantage being tables from a one server could be up-loaded to a second server without worrying about duplicate keys. TIP 10: Monitor port 3306: tcpdump -i eth0 -nN -vvv -xX -s 1500 port 3306 and host not 192.168.1.102 The -s is length of each packet. This monitors all traffic on port 3306 excluding the good client 192.168.1.102. The out will be in the following format: [root@third-fl-71 root]# tcpdump -i eth0 -nN -vvv -xX -s 1500 port 3306 and host not 192.168.1.102 tcpdump: listening on eth0 13:05:01.857705 192.168.1.103.4131 > 192.168.1.71.mysql: S [tcp sum ok] 2542149285:2542149285(0) win 16384 <mss 1460,nop,nop,sackO 0x0000 4500 0030 0b39 4000 8006 6b90 c0a8 0167 E..0.9@...k....g 0x0010 c0a8 0147 1023 0cea 9786 1ea5 0000 0000 ...G.#.......... 0x0020 7002 4000 ebe7 0000 0204 05b4 0101 0402 p.@............. 13:05:04.863552 192.168.1.103.4131 > 192.168.1.71.mysql: S [tcp sum ok] 2542149285:2542149285(0) win 16384 <mss 1460,nop,nop,sackO TIP 11: Create a C or C++ API Download the following: http://www.kitebird.com/mysql-book/sampdb-3ed/sampdb.tar.gz or http://prdownloads.sourceforge.net/souptonuts/mysql_select-0.0.2.tar.gz?download Also reference: http://dev.mysql.com/downloads/other/plusplus/ TIP 12: Connect and Select from Java // // mysql-connector-java-3.0.11-stable-bin.jar or later must be downloaded // and installed from: // http://dev.mysql.com/downloads/connector/j/3.0.html // // Edit to include your username and password: // String userName = "yourusername"; // String password = "passord"; // // // Compile: // javac Select.java // (or you can also use GCC's gcj "gcj -C Select.java") // http://gcc.gnu.org/onlinedocs/gcj/ // http://www.linuxjournal.com/article.php?sid=4860 // http://gcc.gnu.org/java/papers/cni/t1.html // // Run: // java Select // // // The program above assumes "exams" has been created in // the "test" database. If you create "exams" change the // select statment to read: // SELECT pkey,name,exam,score FROM yourdatabase.exams // // // CREATE TABLE exams ( // pkey int(11) NOT NULL auto_increment, // name varchar(15), // exam int, // score int, // PRIMARY KEY (pkey) // // ); // // insert into exams (name,exam,score) values ('Bob',1,75); // insert into exams (name,exam,score) values ('Bob',2,77); // insert into exams (name,exam,score) values ('Bob',3,78); // insert into exams (name,exam,score) values ('Bob',4,80); // // insert into exams (name,exam,score) values ('Sue',1,90); // insert into exams (name,exam,score) values ('Sue',2,97); // insert into exams (name,exam,score) values ('Sue',3,98); // insert into exams (name,exam,score) values ('Sue',4,99); // import java.sql.*; public class Select { public static void main (String[ ] args) { Connection conn = null; String url = "jdbc:mysql://localhost/"; String userName = "username1"; String password = "password1"; try { Class.forName ("com.mysql.jdbc.Driver").newInstance ( ); conn = DriverManager.getConnection (url, userName, password); // System.out.println ("Connected"); Statement s = conn.createStatement ( ); s.executeQuery ("SELECT pkey,name,exam,score FROM test.exams"); ResultSet rs = s.getResultSet ( ); int count = 0; while (rs.next ( )) // loop through rows of result set { int pkey = rs.getInt (1); String name = rs.getString(2); int exam = rs.getInt(3); int score = rs.getInt(4); ++count; System.out.println (count + ",inum: " + pkey + ",name: " + name + ",exam: " + exam + ",score: " + score ); } rs.close ( ); // close result set s.close ( ); // close statement System.out.println (count + " rows were returned"); } catch (Exception e) { System.err.println ("Cannot connect to server"+e); } finally { if (conn != null) { try { conn.close ( ); // System.out.println ("Disconnected"); /* for debugging */ } catch (Exception e) { /* ignore close errors */ } } } } } TIP 13: Print defaults for the current client connection $ my_print_defaults client mysql --port=3306 --socket=/tmp/mysql.sock --no-auto-rehash Note, for client connections, you can put setting in the user's .my.cnf file. This file is located in their home directory. ~/.my.cnf Example file that stores the user and password plus ssl settings that will connect to the remote hosts big.squeezel.com. [client] user=admin password=pass32rD host=big.squeezel.com ssl-ca=/etc/mysql/cacert.pem ssl-cert=/etc/mysql/laptopFOO-cert.pem ssl-key=/etc/mysql/laptopFOO-key.pem Reference tip 38 on setting up ssl connections. TIP 14: Quick Status: mysql> \s -------------- /usr/local/bin/mysql Ver 14.3 Distrib 4.1.1-alpha, for pc-linux (i686) Connection id: 642 Current database: Current user: prog@localhost SSL: Not in use Current pager: stdout Using outfile: '' Using delimiter: ; Server version: 4.1.1-alpha-log Protocol version: 10 Connection: Localhost via UNIX socket Client characterset: latin1_swedish_ci Server characterset: latin1_swedish_ci UNIX socket: /tmp/mysql.sock Uptime: 1 day 15 hours 24 min 38 sec Threads: 1 Questions: 4896 Slow queries: 0 Opens: 14 Flush tables: 1 Open tables: 8 Queries per second avg: 0.035 -------------- TIP 15: "error: 1016: Can't open file:" If it's from an orphaned file, not in the database but on disk, then, the disk file may need to be deleted. myisamchk can help with damaged files. It's best to stop the database. # su - # mysqladmin shutdown # cd /usr/local/var/database # myisamchk * # /etc/init.d/mysql restart TIP 16: Finding records that do not match between two tables. CREATE TABLE bookreport ( b_id int(11) NOT NULL auto_increment, s_id int(11) NOT NULL, report varchar(50), PRIMARY KEY (b_id) ); CREATE TABLE student ( s_id int(11) NOT NULL auto_increment, name varchar(15), PRIMARY KEY (s_id) ); insert into student (name) values ('bob'); insert into bookreport (s_id,report) values ( last_insert_id(),'A Death in the Family'); insert into student (name) values ('sue'); insert into bookreport (s_id,report) values ( last_insert_id(),'Go Tell It On the Mountain'); insert into student (name) values ('doug'); insert into bookreport (s_id,report) values ( last_insert_id(),'The Red Badge of Courage'); insert into student (name) values ('tom'); To find the sudents where are missing reports: select s.name from student s left outer join bookreport b on s.s_id = b.s_id where b.s_id is null; +------+ | name | +------+ | tom | +------+ 1 row in set (0.00 sec) Ok, next suppose there is an orphan record in in bookreport. First delete a matching record in student: delete from student where s_id in (select max(s_id) from bookreport); Now, how to find which one is orphaned: select * from bookreport b left outer join student s on b.s_id=s.s_id where s.s_id is null; +------+------+--------------------------+------+------+ | b_id | s_id | report | s_id | name | +------+------+--------------------------+------+------+ | 4 | 4 | The Red Badge of Courage | NULL | NULL | +------+------+--------------------------+------+------+ 1 row in set (0.00 sec) To clean things up (Note in 4.1 you can't do subquery on same table in a delete so it has to be done in 2 steps): select @t_sid:=b.s_id from bookreport b left outer join student s on b.s_id=s.s_id where s.s_id is null; delete from student where s_id=@t_sid; But, functions do work in delete. For instance the following is possible: delete from student where s_id=max(s_id); It just a problem when joining the table where the delete will occur with another table. Another option is two create a second temp table and locking the first one. TIP 17: Getting a random roll of the dice: CREATE TABLE dice ( d_id int(11) NOT NULL auto_increment, roll int, PRIMARY KEY (d_id) ); insert into dice (roll) values (1); insert into dice (roll) values (2); insert into dice (roll) values (3); insert into dice (roll) values (4); insert into dice (roll) values (5); insert into dice (roll) values (6); select roll from dice order by rand() limit 1; TIP 18: Creating and using your own password file. This assumes MySQL has been configured with SSL support [ ./configure --with-openssl ] CREATE TABLE password ( p_id int(11) NOT NULL auto_increment, id varchar(20), valid enum('y','n'), password BLOB, timeEnter timestamp, PRIMARY KEY (p_id) ); insert into password (id,password) values ('bob',des_encrypt('secret','somekey')); insert into password (id,password) values ('tom',des_encrypt('password','somekey')); insert into password (id,password) values ('kate',des_encrypt('desmark','somekey')); insert into password (id,password) values ('tim',des_encrypt('tim','somekey')); insert into password (id,password) values ('sue',des_encrypt('SUM','somekey')); insert into password (id,password) values ('john',des_encrypt('dotgo86','somekey')); insert into password (id) values ('randal'); mysql> select id,des_decrypt(password,'somekey') from password; +--------+---------------------------------+ | id | des_decrypt(password,'somekey') | +--------+---------------------------------+ | bob | secret | | tom | password | | kate | desmark | | tim | tim | | sue | SUM | | john | dotgo86 | | randal | NULL | +--------+---------------------------------+ 7 rows in set (0.00 sec) Note the bad passwords in the file ('secret','password', and password is the same as the id. The following update statement will fill in the value for valid: update password set valid = COALESCE( concat( substring('y',1, 1-sign(abs( find_in_set( lcase( des_decrypt(password,'somekey')) ,concat('password,secret,simple,',lcase(id),',test')))) ), substring('n',1, sign(abs( find_in_set( lcase( des_decrypt(password,'somekey')) ,concat('password,secret,simple,',lcase(id),',test')))) ) ) ,'n'); Which gives the following: mysql> select id,valid from password; select id,valid from password; +--------+-------+ | id | valid | +--------+-------+ | bob | n | | tom | n | | kate | y | | tim | n | | sue | y | | john | y | | randal | n | +--------+-------+ 7 rows in set (0.00 sec) To understand it, try taking the following select apart: select COALESCE( concat( substring('y',1, 1-sign(abs( find_in_set( lcase( des_decrypt(password,'somekey')) ,concat('password,secret,simple,',lcase(id),',test')))) ), substring('n',1, sign(abs( find_in_set( lcase( des_decrypt(password,'somekey')) ,concat('password,secret,simple,',lcase(id),',test')))) ) ) ,'n') as valid from password; TIP 19: Order in the count: create table a (a varchar(10)); insert into a values ('a'),('a'),('b'),('c'); Note select a,count(a) as count from a group by a order by count; +------+-------+ | a | count | +------+-------+ | b | 1 | | c | 1 | | a | 2 | +------+-------+ 3 rows in set (0.00 sec) but See above name the function ------v select a,count(a) from a group by a order by count(a); ERROR 1111 (HY000): Invalid use of group function TIP 20: Installation: configured for encryption, C API, and user defined functions. ./configure --with-openssl --enable-thread-safe-client --with-mysqld-ldflags=-rdynamic The --with-openssl is very helpful for creating your own password file. Also, if doing C API, having thread safe calls "could" come in handly...it's what I use. See (TIP 27) for user defined functions. Complete Steps: shell> groupadd mysql shell> useradd -g mysql mysql shell> cd mysql-VERSION shell> ./configure --with-openssl --enable-thread-safe-client --with-mysqld-ldflags=-rdynamic shell> make shell> make install shell> cp support-files/my-medium.cnf /etc/my.cnf shell> cd /usr/local/mysql shell> bin/mysql_install_db --user=mysql shell> chown -R root . shell> chown -R mysql var shell> chgrp -R mysql . shell> bin/mysqld_safe --user=mysql & See (TIP 25) for configuring the log-bin and log files in /etc/my.cnf Installing mysql so that it will startup automatically. This also enables it to be restarted, "/etc/init/mysql restart". cp ./support-files/mysql.server /etc/init.d/mysql cd /etc/rc3.d ln -s ../init.d/mysql S85mysql ln -s ../init.d/mysql K85mysql cd /etc/rc5.d ln -s ../init.d/mysql S85mysql ln -s ../init.d/mysql K85mysql cd ../init.d chmod 755 mysql Deleting any blank users or passwords, and creating a valid user is shown below. STEP 1: First, connect to the mysql database with the connect command: mysql> connect mysql; STEP 2: Next, delete all blank accounts and/or global host listing: mysql> DELETE FROM user WHERE User = ''; mysql> DELETE FROM db WHERE Host = '%'; STEP 3: Delete any accounts with blank passwords: mysql> DELETE FROM user where password=''; STEP 4: Create a valid admin account. The example here creates admin1. mysql> GRANT ALL PRIVILEGES ON *.* TO admin1@localhost IDENTIFIED BY 's3cr3tpass45' WITH GRANT OPTION; or if you want the account to get access from any host. mysql> GRANT ALL PRIVILEGES ON *.* TO admin1@"%" IDENTIFIED BY 's3cr3tpass45' WITH GRANT OPTION; STEP 5: Restart the server "/etc/init.d/mysql restart" TIP 21: Getting 1 matching row from an OUTER join CREATE TABLE parent ( pkey int(11) NOT NULL auto_increment, pname varchar(5), timeEnter timestamp, PRIMARY KEY (pkey) ); CREATE TABLE child ( ckey int(11) NOT NULL auto_increment, pkey int(11) NOT NULL, cname varchar(5), timeEnter timestamp, PRIMARY KEY (ckey) ); insert into parent(pname) values ('A'); select @a_lid:=last_insert_id(); insert into child(pkey,cname) values (@a_lid,'a1'); insert into child(pkey,cname) values (@a_lid,'a2'); insert into child(pkey,cname) values (@a_lid,'a3'); insert into parent(pname) values ('B'); select @a_lid:=last_insert_id(); insert into child(pkey,cname) values (@a_lid,'b1'); insert into child(pkey,cname) values (@a_lid,'b2'); insert into parent(pname) values ('C'); mysql> select p.*,c.cname,count(c.pkey) as number from parent p left outer join child c on p.pkey=c.pkey where c.pkey is not null group by c.pkey; +------+-------+---------------------+-------+--------+ | pkey | pname | timeEnter | cname | number | +------+-------+---------------------+-------+--------+ | 5 | A | 2004-04-28 09:56:59 | a1 | 3 | | 6 | B | 2004-04-28 09:56:59 | b1 | 2 | +------+-------+---------------------+-------+--------+ 2 rows in set (0.01 sec) For comparison, here is a listing of all the matching data: mysql> select * from parent p left outer join child c on p.pkey=c.pkey where c.pkey is not null; select * from parent p left outer join child c on p.pkey=c.pkey where c.pkey is not null; +------+-------+---------------------+------+------+-------+---------------------+ | pkey | pname | timeEnter | ckey | pkey | cname | timeEnter | +------+-------+---------------------+------+------+-------+---------------------+ | 5 | A | 2004-04-28 09:56:59 | 7 | 5 | a1 | 2004-04-28 09:56:59 | | 5 | A | 2004-04-28 09:56:59 | 8 | 5 | a2 | 2004-04-28 09:56:59 | | 5 | A | 2004-04-28 09:56:59 | 9 | 5 | a3 | 2004-04-28 09:56:59 | | 6 | B | 2004-04-28 09:56:59 | 10 | 6 | b1 | 2004-04-28 09:56:59 | | 6 | B | 2004-04-28 09:56:59 | 11 | 6 | b2 | 2004-04-28 09:56:59 | +------+-------+---------------------+------+------+-------+---------------------+ 5 rows in set (0.00 sec) TIP 22: Getting a virtual row count. Assume the following table: CREATE TABLE student ( s_id int(11) NOT NULL auto_increment, name varchar(15), PRIMARY KEY (s_id) ); Add some rows and delete (just to convice you this works in all cases) insert into student (name) values ('tom'); insert into student (name) values ('bob'); insert into student (name) values ('sue'); insert into student (name) values ('mike'); insert into student (name) values ('joe'); insert into student (name) values ('zoe'); insert into student (name) values ('harpo'); delete from student where name = 'bob'; Now, note mc is the row count...independent of s_id; select a.name,sum(1) as mc from student a, student b where a.s_id <= b.s_id group by a.s_id, a.name order by mc; +-------+------+ | name | mc | +-------+------+ | harpo | 1 | | zoe | 2 | | joe | 3 | | mike | 4 | | sue | 5 | | tom | 6 | +-------+------+ 6 rows in set (0.00 sec) mysql> *Note: SEE ( TIP 27 ), using the sequence function. TIP 23: Computing running and sliding aggregates. Assume the following table and data: CREATE TABLE dice ( d_id int(11) NOT NULL auto_increment, roll int, PRIMARY KEY (d_id) ); insert into dice (roll) values (1); insert into dice (roll) values (2); insert into dice (roll) values (3); insert into dice (roll) values (4); insert into dice (roll) values (5); insert into dice (roll) values (6); The following gives a running sum: mysql> select a.roll, sum(b.roll) from dice a, dice b where b.d_id <= a.d_id group by a.d_id, a.roll; +------+-------------+ | roll | sum(b.roll) | +------+-------------+ | 1 | 1 | | 2 | 3 | | 3 | 6 | | 4 | 10 | | 5 | 15 | | 6 | 21 | +------+-------------+ 6 rows in set (0.00 sec) Note, it's also possible to get a running average by changing the sum to avg as follows: mysql> select a.roll, avg(b.roll) from dice a, dice b where b.d_id <= a.d_id group by a.d_id, a.roll; +------+-------------+ | roll | avg(b.roll) | +------+-------------+ | 1 | 1.0000 | | 2 | 1.5000 | | 3 | 2.0000 | | 4 | 2.5000 | | 5 | 3.0000 | | 6 | 3.5000 | +------+-------------+ 6 rows in set (0.00 sec) TIP 24: What commands were executed? Reading the log files. (By default on 4.1.2 is should be setup, but, see TIP 25 to check.) The following is an example of the "show binlog events" which will show all the inserted and deleted commands. See "TIP 2:" which shows how to clean up or reset with the "reset master". mysql> show binlog events; show binlog events; +------------------------+-----+------------+-----------+--------------+--------------------------------------------+ | Log_name | Pos | Event_type | Server_id | Orig_log_pos | Info | +------------------------+-----+------------+-----------+--------------+--------------------------------------------+ | third-fl-71-bin.000001 | 4 | Start | 1 | 4 | Server ver: 4.1.1-alpha-log, Binlog ver: 3 | | third-fl-71-bin.000001 | 79 | Query | 1 | 79 | use `test`; create table j2 (a int) | | third-fl-71-bin.000001 | 137 | Query | 1 | 137 | use `test`; insert into j2 (a) values (3) | | third-fl-71-bin.000001 | 201 | Query | 1 | 201 | use `test`; insert into j2 (a) values (9) | | third-fl-71-bin.000001 | 265 | Query | 1 | 265 | use `test`; delete from j2 where a=3 | +------------------------+-----+------------+-----------+--------------+--------------------------------------------+ 5 rows in set (0.00 sec) Note that the logfiles by default are located in "/usr/local/var" (see TIP 25:) or execute "mysql> show variables" and look for the entry under the datadir. It's possible to query specific logfiles if they exist: mysql> show binlog events in 'third-fl-71-bin.000001'; It's also possible to specify the start position and limit the number of records as follows: mysql> show binlog events from 201 limit 2; show binlog events from 201 limit 2; +------------------------+-----+------------+-----------+--------------+-------------------------------------------+ | Log_name | Pos | Event_type | Server_id | Orig_log_pos | Info | +------------------------+-----+------------+-----------+--------------+-------------------------------------------+ | third-fl-71-bin.000001 | 201 | Query | 1 | 201 | use `test`; insert into j2 (a) values (9) | | third-fl-71-bin.000001 | 265 | Query | 1 | 265 | use `test`; delete from j2 where a=3 | +------------------------+-----+------------+-----------+--------------+-------------------------------------------+ 2 rows in set (0.00 sec) Or, from the command line: $ mysqlbinlog <logfile> Another option is writing a C api. For a complete example of this (selectbinlog.c) download the following: http://prdownloads.sourceforge.net/souptonuts/mysql_select-0.0.1.tar.gz?download or take a peek at http://souptonuts.sourceforge.net/code/selectbinlog.c.html This sample "selectbinlog.c" selects only the "Query" events. The code is pretty simple. FYI: If you do a lot of tracking, you may want to write the information to a Berkeley DB. Contrary to the name Berkeley DB is not a database but a hash, or there is an option for b-tree format. MySQL can use Berkeley DB for the underlying table structure. It's very fast, and you won't get logs of your logs. If you're using Linux, Berkeley DB is already installed on your system. Ok, so how does one use Berkeley DB? Samples can be found at the following link. Look for berkeleydb_0.x.x.tar.gz at the following link http://sourceforge.net/project/showfiles.php?group_id=79066&package_id=80379 The newer version of Berkeley DB also supports encryption. Berkeley DB is open source and can be downloaded from the following: http://www.sleepycat.com/ NOTE: MySQL uses Berkeley DB if configured for it ./configure --with-berkeley-db And tables are created with the "ENGINE" or "TYPE" option: CREATE TABLE b (i INT) ENGINE = BDB; or CREATE TABLE b (i INT) TYPE = BDB; TIP 25: Setting the binary log file. This can be configured in /etc/my.cnf # The MySQL server [mysqld] port = 3306 socket = /tmp/mysql.sock log-bin = /usr/local/var/mysqlLOGb.log log = /usr/local/var/mysqlLOG.log or for the default hostname just log-bin [mysqld] port = 3306 socket = /tmp/mysql.sock log-bin IMPORTANT: The default my.cnf has a "log-bin" entry. Make sure it is not listed twice. It's also possible to set the text log file. Note both "log-bin" and "log" are set here: [mysqld] port = 3306 socket = /tmp/mysql.sock log-bin = /usr/local/var/mysqlLOGb.log log = /usr/local/var/mysqlLOG.log Note, (see TIP 24:) the binary log file works with the "show binlog events command" and shows, updates, creates, deletes, and drops, but no select statements. In contrast, the text log-file "/usr/local/var/mysqlLOG.log" shows the user, and the select statement, all of the above, but it's in a text file. I believe the text format is going away with version 5.0. The following command "DOES NOT" give information about these log files: mysql> show logs; This is only for Berkeley DB type databases before commit on this type of table. It's not what you want! TIP 26: Free articles and tutorials on normalization. a) http://dev.mysql.com/tech-resources/articles/intro-to-normalization.html b) http://www.phpbuilder.com/columns/barry20000731.php3?page=1 c) http://support.microsoft.com/default.aspx?scid=http://support.microsoft.com:80/support/kb/articles/q100/1/39.asp&NoWebContent=1&NoWebContent=1 d) http://www.gslis.utexas.edu/~l384k11w/normstep.html f) http://www.sims.berkeley.edu/academics/courses/is202/f97/Lecture8/ g) http://www.microsoft-accesssolutions.co.uk/higher_norm_form.htm h) http://ocw.mit.edu/OcwWeb/Civil-and-Environmental-Engineering/1-264JDatabase--Internet--and-Systems-Integration-TechnologiesFall2002/LectureNotes/index.htm TIP 27: Adding and Compiling a User-Defined function. Here are some examples that can be compiled and used with MySQL 4.1. See below for how to install. First, just a taste of what they look like: mysql> select lookup("www.yahoo.com"); select lookup("www.yahoo.com"); +-------------------------+ | lookup("www.yahoo.com") | +-------------------------+ | 216.109.118.71 | +-------------------------+ 1 row in set (0.02 sec) and mysql> select reverse_lookup("216.109.118 select reverse_lookup("216.109.118.79"); +----------------------------------+ | reverse_lookup("216.109.118.79") | +----------------------------------+ | p16.www.dcn.yahoo.com | +----------------------------------+ 1 row in set (0.02 sec) Also mysql> select sequence(3); select sequence(3); +-------------+ | sequence(3) | +-------------+ | 4 | +-------------+ 1 row in set (0.01 sec) mysql> select sequence(sequence(3)); select sequence(sequence(3)); +-----------------------+ | sequence(sequence(3)) | +-----------------------+ | 5 | +-----------------------+ 1 row in set (0.00 sec) mysql> select sequence(3.4); select sequence(3.4); +---------------+ | sequence(3.4) | +---------------+ | 4 | +---------------+ 1 row in set (0.00 sec) mysql> create table junk (a varchar(1)); mysql> insert into junk (a) values ('a'),('b'),('c'),('d'),('e'); mysql> select sequence(),a from junk; select sequence(),a from junk; +------------+------+ | sequence() | a | +------------+------+ | 1 | a | | 2 | b | | 3 | c | | 4 | d | | 5 | e | +------------+------+ 5 rows in set (0.00 sec) An example of an aggregate function: mysql> create table cost (inum int, cost double); create table cost (inum int, cost double); Query OK, 0 rows affected (0.00 sec) mysql> insert into cost (inum,cost) values (3,4.5); insert into cost (inum,cost) values (3,4.5); Query OK, 1 row affected (0.00 sec) mysql> insert into cost (inum,cost) values (10,21.3); insert into cost (inum,cost) values (10,21.3); Query OK, 1 row affected (0.00 sec) mysql> select avgcost(inum,cost) from cost; select avgcost(inum,cost) from cost; +--------------------+ | avgcost(inum,cost) | +--------------------+ | 17.4231 | +--------------------+ 1 row in set (0.00 sec) OK, HOW TO COMPILE: For best results mysql-4.1.2-alpha or above configured with the following option: --with-mysqld-ldflags=-rdynamic The full line of my configure is as follows since I use openssl as well. STEP A: ./configure --with-openssl --enable-thread-safe-client --with-mysqld-ldflags=-rdynamic make make install /etc/init.d/mysql restart (Note: if "/etc/init.d/mysql" does not exist see (TIP 20:) ) STEP B: Under "mysql-4.1.2-alpha/sql" issue the following command. # make udf_example.so STEP C: As root copy the file to a directory where mysql can find it. # cp udf_example.so /usr/lib/udf_example.so STEP D: Load mysql. You may want to look at udf_example.cc, since it as instructions as well. From here issue the following commands: mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "udf_example.so"; mysql> CREATE FUNCTION myfunc_double RETURNS REAL SONAME "udf_example.so"; mysql> CREATE FUNCTION myfunc_int RETURNS INTEGER SONAME "udf_example.so"; mysql> CREATE FUNCTION sequence RETURNS INTEGER SONAME "udf_example.so"; mysql> CREATE FUNCTION lookup RETURNS STRING SONAME "udf_example.so"; mysql> CREATE FUNCTION reverse_lookup RETURNS STRING SONAME "udf_example.so"; mysql> CREATE AGGREGATE FUNCTION avgcost RETURNS REAL SONAME "udf_example.so"; And the functions can be deleted by the following: mysql> DROP FUNCTION metaphon; mysql> DROP FUNCTION myfunc_double; mysql> DROP FUNCTION myfunc_int; mysql> DROP FUNCTION lookup; mysql> DROP FUNCTION reverse_lookup; mysql> DROP FUNCTION avgcost; That's it. Just run the functions above. These can serve as templates for writing your own. TIP 28: Loading Data into Tables from Text Files. Assume you have the following table. CREATE TABLE loadtest ( pkey int(11) NOT NULL auto_increment, name varchar(20), exam int, score int, timeEnter timestamp(14), PRIMARY KEY (pkey) ); And you have the following formatted text file as shown below with the unix "tail" command: $ tail /tmp/out.txt 'name22999990',2,94 'name22999991',3,93 'name22999992',0,91 'name22999993',1,93 'name22999994',2,90 'name22999995',3,93 'name22999996',0,93 'name22999997',1,89 'name22999998',2,85 'name22999999',3,88 NOTE: loadtest contains the "pkey" and "timeEnter" fields which are not present in the "/tmp/out.txt" file. Therefore, to successfully load the specific fields issue the following: mysql> load data infile '/tmp/out.txt' into table loadtest fields terminated by ',' (name,exam,score); TIP 29: Referential Integrity with InnoDB tables. STEP 1 (First create the tables as InnoDB) CREATE TABLE agents ( akey INTEGER NOT NULL auto_increment PRIMARY KEY, ln varchar(30), fn varchar(25), phone varchar(20), timeEnter timestamp(14)) ENGINE = InnoDB; CREATE TABLE clients ( ckey INTEGER NOT NULL auto_increment PRIMARY KEY, f_akey INTEGER NOT NULL, ln varchar(30), fn varchar(25), phone varchar(20), FOREIGN KEY (f_akey) REFERENCES agents(akey)) ENGINE = InnoDB; STEP 2 (Insert entries -- successful way). mysql> insert into agents (ln,fn,phone) values ('Anderson','Bob','215-782-2134'); mysql> select @ckey:=last_insert_id(); mysql> insert into clients (f_akey,ln,fn,phone) values (@ckey,'Chirico','Abby','215-782-2353'); myslq> insert into clients (f_akey,ln,fn,phone) values (@ckey,'Payne','Zoe','215-782-2352'); The "last_insert_id()" must be assigned to a variable, because the client entries for the two client keys have the same agent. After the first insert into the client table "last_insert_id()" is incremented, reflecting the new add to the client table. STEP 3 (Try to insert a client record without a matching agent -- unsuccessful way) mysql> insert into agents (ln,fn,phone) values ('Splat','Sporkey','215-782-9987'); Above is ok myslq> insert into clients (f_akey,ln,fn,phone) values (last_insert_id(),'Landis','Susan','215-782-5222'); Above Ok for the first record, but, below last_insert_id() has been incremented and the insert will be incorrect. And probably fail, if there is no matching "akey" in agents. myslq> insert into clients (f_akey,ln,fn,phone) values (last_insert_id(),'Landis','Brian','215-782-5222'); SPECIAL NOTE (The "clients" table must be dropped before the "agents" table) TIP 30: Is it Possible to do Incremental Backups? And is it possible to restore changes for only one user? See TIP 24 and TIP 25 for setting up and using "binlog" and the text log. NOTE: "mysql> show logs;" IS NOT a status on these log files -- it's only for Berkeley DB. From the shell prompt "mysqlbinlog" will list all the changes. Note your binary log file may be in a different directory, and have a different name depending on the setting in /etc/my.cnf $ mysqlbinlog /usr/local/var/mysqlLOGbin.000001 #040616 8:41:23 server id 1 log_pos 17465 Query thread_id=384 SET TIMESTAMP=1087389683; CREATE TABLE exams ( pkey int(11) NOT NULL auto_increment, name varchar(15) default NULL, exam int(11) default NULL, score int(11) default NULL, PRIMARY KEY (pkey) ) ENGINE=MyISAM DEFAULT CHARSET=latin1; # at 17761 #040616 8:41:50 server id 1 log_pos 17761 Intvar SET INSERT_ID=1; # at 17789 #040616 8:41:50 server id 1 log_pos 17789 Query thread_id=384 SET TIMESTAMP=1087389710; insert into exams (name,exam,score) values ('Bob',1,75); # at 17879 #040616 8:41:50 server id 1 log_pos 17879 Intvar ....[SNIPPED] # at 18615 #040616 8:41:50 server id 1 log_pos 18615 Query thread_id=384 SET TIMESTAMP=1087389710; insert into exams (name,exam,score) values ('Sue',4,99); # at 18705 #040616 8:52:35 server id 1 log_pos 18705 Intvar SET INSERT_ID=23000010; # at 18733 # LOAD DATA INFILE '/tmp/out.txt' INTO TABLE `loadtest` FIELDS TERMINATED BY ','..[SNIPPED] # file_id: 1 block_len: 200 Note the thread_id "384", session "040616", TIMESTAMP vales, and actual sql statements. With grep, awk, or sed it's possible to weed out unwanted queries. This assumes you have a base, or a "full restore" starting point. Compare above to the actual commands listed here: CREATE TABLE exams ( pkey int(11) NOT NULL auto_increment, name varchar(15) default NULL, exam int(11) default NULL, score int(11) default NULL, PRIMARY KEY (pkey) ) ENGINE=MyISAM; insert into exams (name,exam,score) values ('Bob',1,75); insert into exams (name,exam,score) values ('Bob',2,77); insert into exams (name,exam,score) values ('Bob',3,78); insert into exams (name,exam,score) values ('Bob',4,80); insert into exams (name,exam,score) values ('Sue',1,90); insert into exams (name,exam,score) values ('Sue',2,97); insert into exams (name,exam,score) values ('Sue',3,98); insert into exams (name,exam,score) values ('Sue',4,99); mysql> load data infile '/tmp/out.txt' into table exams fields terminated by ',' (name,exam,score); TIP 31: Getting XML and HTML output. Assume you have the table "exams" in the database "test". Then, the following will give you XML output if executed from the shell prompt with the "-X" option. For html output use the "-H" option. $ mysql -X -e "select * from exams" test <?xml version="1.0"?> <resultset statement="select * from exams "> <row> <pkey>1</pkey> <name>Bob</name> <exam>1</exam> <score>75</score> </row> <row> <pkey>2</pkey> <name>Bob</name> <exam>2</exam> <score>77</score> </row> <row> <pkey>3</pkey> <name>Bob</name> <exam>3</exam> <score>78</score> </row> <row> <pkey>4</pkey> <name>Bob</name> <exam>4</exam> <score>80</score> </row> <row> <pkey>5</pkey> <name>Sue</name> <exam>1</exam> <score>90</score> </row> </resultset> Or, (-N is depreciated so use --skip-column-names ) for no heading: $ mysql --skip-column-names -e "select * from exams" test +---+------+------+------+ | 1 | Bob | 1 | 75 | | 2 | Bob | 2 | 77 | | 3 | Bob | 3 | 78 | | 4 | Bob | 4 | 80 | | 5 | Sue | 1 | 90 | | 6 | Sue | 2 | 97 | | 7 | Sue | 3 | 98 | | 8 | Sue | 4 | 99 | +---+------+------+------+ And, add the "-s" silent option to get the following: $ mysql --skip-column-names -s -e "select * from exams" test 1 Bob 1 75 2 Bob 2 77 3 Bob 3 78 4 Bob 4 80 5 Sue 1 90 6 Sue 2 97 7 Sue 3 98 8 Sue 4 99 To prevent being prompted for a password. Create "/home/chirico/.my.cnf" with password and user. An example is shown below. Unless a user is entered "piggy" it will default to "chirico", this user. [client] user=piggy password=p1ggyp1ssw6r5 Use this method. It will not show up when doing "ps -aux" TIP 32: Views? Can you do a "create view" in MySQL? No. Not until version 5. TIP 33: Spatial Extensions - MySQL 4.1 supports spatial extensions. Getting the X value of a point. mysql> SELECT X(GeomFromText('Point(5.02 7.9)')); +------------------------------------+ | X(GeomFromText('Point(5.02 7.9)')) | +------------------------------------+ | 5.02 | +------------------------------------+ 1 row in set (0.00 sec) Note that a comma separates points, and the x,y values are separated by spaces. Getting the length of a line. (1 1) / / / (0 0) mysql> SELECT GLength(GeomFromText('LineString(0 0,1 1)')); +----------------------------------------------+ | GLength(GeomFromText('LineString(0 0,1 1)')) | +----------------------------------------------+ | 1.4142135623731 | +----------------------------------------------+ Getting the total length of all the lines making a step. (2 1) ---- (2 2) | | (1 0) ---- (1 1) | | (0 0) mysql> SELECT GLength(GeomFromText('LineString(0 0,1 0,1 1,1 2,2 2)')); +----------------------------------------------------------+ | GLength(GeomFromText('LineString(0 0,1 0,1 1,1 2,2 2)')) | +----------------------------------------------------------+ | 4 | +----------------------------------------------------------+ Or the perimiter of the following triangle: (1 1) / \ / \ (0 0) /________ \ (2 0) mysql> SELECT GLength(GeomFromText('LineString(0 0,1 1,2 0,0 0)')); +------------------------------------------------------+ | GLength(GeomFromText('LineString(0 0,1 1,2 0,0 0)')) | +------------------------------------------------------+ | 4.8284271247462 | +------------------------------------------------------+ Note the following select statement is a 5x5 square with left bottom point at 0 0. (5 0) (5 5) ----------- | | | | | | | | ----------- (0 0) (0 5) mysql> SELECT Area(GeomFromText('Polygon((0 0,0 5,5 5,5 0,0 0))')); +------------------------------------------------------+ | Area(GeomFromText('Polygon((0 0,0 5,5 5,5 0,0 0))')) | +------------------------------------------------------+ | 25 | +------------------------------------------------------+ 1 row in set (0.00 sec) The area of the inner square "9" minus the area of the outer square "25" is "16". 5 0 ------------------ 5 5 | 4 1 4 4 | | ---------- | | | | | | | | | | | | | | | | | | ---------- | | 1 1 1 4 | 0 0 ------------------ 0 5 mysql> SELECT Area(GeomFromText('Polygon((0 0,0 5,5 5,5 0,0 0),(1 1,1 4,4 4,4 1,1 1))')); +----------------------------------------------------------------------------+ | Area(GeomFromText('Polygon((0 0,0 5,5 5,5 0,0 0),(1 1,1 4,4 4,4 1,1 1))')) | +----------------------------------------------------------------------------+ | 16 | +----------------------------------------------------------------------------+ 1 row in set (0.00 sec) Reference: http://dev.mysql.com/doc/mysql/en/Spatial_extensions_in_MySQL.html http://mysql.planetmirror.com/doc/mysql/en/Populating_spatial_columns.html http://www.ctch.net/mysql/manual_Spatial_extensions_in_MySQL.html TIP 34: Creating Tables for Spatial Extensions. mysql> CREATE TABLE spat (p POINT, g POLYGON, l LINESTRING, geo GEOMETRY ); Note, GEOMETRY is general and will take the following values: - POINT - POLYGON - LINESTRING - MULTIPOINT - MULTILINESTRING - MULTIPOLYGON - GEOMETRYCOLLECTION Inserting values. mysql> INSERT INTO spat (p) VALUES (GeomFromText('POINT(1 2)')); Displaying values: mysql> select X(p),Y(p) from spat; +------+------+ | X(p) | Y(p) | +------+------+ | 1 | 2 | +------+------+ Note with "geo" it's possible to insert combinations mysql> insert into spat(geo) values (GeomFromText('MULTIPOLYGON(((0 0,10 0,10 10,0 10,0 0)),((5 5,7 5,7 7,5 7, 5 5)))')); Now, to see what's in "geo", do the following: mysql> select AsText(geo) from spat; +-------------------------------------------------------------------+ | AsText(geo) | +-------------------------------------------------------------------+ | POINT(1 2) | | MULTIPOLYGON(((0 0,10 0,10 10,0 10,0 0)),((5 5,7 5,7 7,5 7,5 5))) | +-------------------------------------------------------------------+ 2 rows in set (0.02 sec) TIP 35: Working with Spatial Relationship Functions. ... example will follow TIP 36: Difficult Column Names, Like `DATE` -- use backtick. If using "date" as a column name, enclose it in backticks ` as follows: CREATE TABLE IF NOT EXISTS stocks ( pkey int(11) NOT NULL auto_increment, `date` date, ticker varchar(5), open float, high float, low float, close float, volume int, timeEnter timestamp(14), PRIMARY KEY (pkey) ) ; To get 1 day old data reference: http://biz.swcp.com/stocks/#Daily update Statement to load data: mysql> load data infile '/tmp/sp500hst.txt' into table stocks fields terminated by ',' (date,ticker,open,high,low,close,volume); TIP 37: Setting up MASTER and SLAVE replication. The master will need to have binary logging turned on. MASTER (These steps are performed on the mysql installation that you have designated as the MASTER). Binary logging needs to be turned on. Under the [mysqld] section in the my.cnf file add log-bin. You can assign this value to a file. If you assign it to a file, make sure the directory exists. My master IP address is 192.168.1.12 with hostname big.squeezel.com. Step 1. Turn on binary logging. Create the necessary directories. $ mkdir -p /var/mysql /etc/my.cnf [mysqld] log-bin=/var/mysql/mysqlLOGM.log Step 2. Restart mysql. $ /etc/init.d/mysqld restart Step 3. Create an account on the master that has access to the tables that will be replicated. mysql> GRANT ALL PRIVILEGES ON *.* TO admin1@"%" IDENTIFIED BY 's3cr3tpass45' WITH GRANT OPTION; Step 4. Login to mysql and run the "show master status" command. mysql> show master status; +------------------+----------+--------------+------------------+ | File | Position | Binlog_Do_DB | Binlog_Ignore_DB | +------------------+----------+--------------+------------------+ | mysqlLOGb.000021 | 270 | | | +------------------+----------+--------------+------------------+ 1 row in set (0.00 sec) Note the name of the file. In my case it is "mysqlLOGb.000021" and the position. In my case the position is 270. This position will update with changes to you database. You want a quit master to setup master slave replication. SLAVE (These steps are performed on the mysql installation that you have designated as the SLAVE). Binary logging does not have to be turned on; however, it doesn't hurt. If you want all updates logged on the slave, including the ones from the master. Then, use log-slave-updates. Step 1. Turn on binary logging, including the log-slave-updates. Create necessary directories, and assign a unique server-id. $ mkdir -p /var/mysql The following changes are made in the my.cnf file. By default this is located in /etc/my.cnf /etc/my.cnf [mysqld] log-bin=/var/mysql/mysqlLOGS30.log log-slave-updates server-id=30 Step 2. From mysql, in the slave, put in the IP of the Master or the hostname. mysql> CHANGE MASTER TO MASTER_HOST='big.squeezel.com', MASTER_USER='admin1', MASTER_PASSWORD='s3cr3tpass45', MASTER_LOG_FILE='mysqlLOGb.000021', MASTER_LOG_POS=270; START SLAVE; show slave status; This will only log future changes from the point that you implemented the change above. If you want to get all past changes, execute the following command. mysql> LOAD DATA FROM MASTER; Problems: 1. Make sure the slave can get access to the master. The account must allow outside access. Note the grant command above admin1@"%". 2. Sometimes the slave will not catch the changes. You must stop the slave. mysql> stop slave; Then, run the CHANGE MASTER command above with the correct file name and position. References: http://dev.mysql.com/doc/refman/5.0/en/load-data-from-master.html TIP 38: Setting up ssl connections. Step 1. Create your own CA. This example is done on Fedora Core 6 as root. Note, I'm using password: "password123", and filling in the request for Country Name "US", State "Pennsylvania" respectively. However, the extra challenge password is not filled out. Instead, I have just hit return on this option. It's very important to record the responses to the questions. Do it in an emacs session, since you'll need this information when signing and generating certificates. [root@livingroom ~]# cd [root@livingroom ~]# mkdir -p /root/certs/mysql/CA [root@livingroom CA]# /etc/pki/tls/misc/CA -newca /etc/pki/tls/misc/CA -newca CA certificate filename (or enter to create) Making CA certificate ... Generating a 1024 bit RSA private key .........................++++++ ...............................++++++ writing new private key to '../../CA/private/./cakey.pem' Enter PEM pass phrase:password123 Verifying - Enter PEM pass phrase:password123 ----- You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [GB]:US US State or Province Name (full name) [Berkshire]:Pennsylvania Pennsylvania Locality Name (eg, city) [Newbury]:Elkins Park Elkins Park Organization Name (eg, company) [My Company Ltd]:chirico_Widgets chirico_Widgets Organizational Unit Name (eg, section) []:chirico_Widgets chirico_Widgets Common Name (eg, your name or your server's hostname) []:livingroom.squeezel.com livingroom.squeezel.com Email Address []:chirico@livingroom.mchirico.org chirico@livingroom.mchirico.org Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []: An optional company name []: Using configuration from /etc/pki/tls/openssl.cnf Enter pass phrase for ../../CA/private/./cakey.pem:password123 Check that the request matches the signature Signature ok Certificate Details: Serial Number: 0 (0x0) Validity Not Before: Jan 16 16:21:25 2007 GMT Not After : Jan 15 16:21:25 2010 GMT Subject: countryName = US stateOrProvinceName = Pennsylvania organizationName = chirico_Widgets organizationalUnitName = chirico_Widgets commonName = livingroom.squeezel.com emailAddress = chirico@livingroom.mchirico.org X509v3 extensions: X509v3 Basic Constraints: CA:FALSE Netscape Comment: OpenSSL Generated Certificate X509v3 Subject Key Identifier: 95:33:77:BA:B9:7A:EE:4C:B0:0C:49:1F:56:93:ED:CA:AE:19:9C:49 X509v3 Authority Key Identifier: keyid:95:33:77:BA:B9:7A:EE:4C:B0:0C:49:1F:56:93:ED:CA:AE:19:9C:49 Certificate is to be certified until Jan 15 16:21:25 2010 GMT (1095 days) Write out database with 1 new entries Data Base Updated [root@livingroom CA]# Step 2. Adjust CA expiration, if desired. Change the number of days the certificate is good for. Note above, this certificate is good for 1095 days. Which is fine, but if you needed to extend this, you can do it with the following command. [root@livingroom mysql]# openssl x509 -in ../CA/cacert.pem -days 3650 -out cacert.pem -signkey ../CA/private/cakey.pem Getting Private key Enter pass phrase for ../CA/private/cakey.pem:password123 Step 3. Create Server Certificates. Here I'm generating two certificates. One for the computer livingroom, and one for the computer big.squeezel.com. Generate a unique certificate for each of your servers. # mkdir server_certs # openssl req -new -nodes \ -subj '/CN=livingroom.squeezel.com/O=chirico_Widgets/C=US/ST=Pennsylvania/L=Elkins Park/emailAddress=chirico@livingroom.mchirico.org'\ -keyout livingroomFOO-key.pem -out livingroomFOO-req.pem -days 3650 # openssl req -new -nodes \ -subj '/CN=big.squeezel.com/O=chirico_Widgets/C=US/ST=Pennsylvania/L=Elkins Park/emailAddress=chirico@livingroom.mchirico.org'\ -keyout bigFOO-key.pem -out bigFOO-req.pem -days 3650 Step 4. Sign the certificates. You'll be asked for the password during this step. # openssl ca -days 3650 -out livingroomFOO-cert.pem -infiles livingroomFOO-req.pem # openssl ca -days 3650 -out bigFOO-cert.pem -infiles bigFOO-req.pem Step 5. Create a directory for the certs "/etc/mysql" and copy the files. # mkdir -p /etc/mysql # cp /root/certs/CA/cacert.pem /etc/mysql/. # cp /root/certs/mysql/server_certs/*.pem /etc/mysql/. Step 6. Edit mysql my.cnf file. In may case it is "/etc/my.cnf" [mysqld] ssl-ca=/etc/mysql/cacert.pem ssl-cert=/etc/mysql/livingroomFOO-cert.pem ssl-key=/etc/mysql/livingroomFOO-key.pem Step 7. Restart mysql # /etc/init.d/mysqld restart Step 8. Create a user that requires ssl. This is done in mysql. Do this for each client that will need to connect. mysql> grant all privileges on *.* to 'admin'@'localhost' identified by 'pass32rD' require ssl; mysql> grant all privileges on *.* to 'admin'@'big.squeezel.com' identified by 'pass32rD' require ssl; Step 9. Create the user's ".my.cnf" file. For example, for user chirico, the following file is created. Note how the two servers differ. This is done of server livingroom for user chirico. [chirico@livingroom ~]$ cat /home/chirico/.my.cnf [client] user=admin password=pass32rD ssl-ca=/etc/mysql/cacert.pem ssl-cert=/etc/mysql/livingroomFOO-cert.pem ssl-key=/etc/mysql/livingroomFOO-key.pem [chirico@big ~]$ cat /home/zchirico/.my.cnf [client] user=admin password=pass32rD ssl-ca=/etc/mysql/cacert.pem ssl-cert=/etc/mysql/bigFOO-cert.pem ssl-key=/etc/mysql/bigFOO-key.pem Step 10. Connect to the server. [chirico@big ~]$ mysql --host=livingroom.squeezel.com If you can a value for the Ssl_cipher after you connected, then, your connection is secure. mysql> SHOW STATUS LIKE 'Ssl_cipher'; +---------------+--------------------+ | Variable_name | Value | +---------------+--------------------+ | Ssl_cipher | DHE-RSA-AES256-SHA | +---------------+--------------------+ 1 row in set (0.00 sec) Notes: If you're looking for ssl C API examples, download the link below and reference the example capi/stmt_exec_ssl.c http://www.kitebird.com/mysql-book/sampdb-3ed/sampdb.tar.gz TIP 39: mysqlshow - A command run from the command prompt that will quickly display database, table and column information. [chirico@big mysql]$ mysqlshow +--------------------+ | Databases | +--------------------+ | information_schema | | admin | | mysql | | test | +--------------------+ mysql_config - Displays compile time options. Inaddition to what is also shown below, it can be used to show socket, version and cflags information. [chirico@big mysql]$ mysql_config --libs -L/usr/lib64/mysql -lmysqlclient -lz -lcrypt -lnsl -lm -L/usr/lib64 -lssl -lcrypto [chirico@big mysql]$ mysql_config --include -I/usr/include/mysql TIP 40: Queries through ssh. The server may have port 3306 closed to the outside and or access is only granted for local accounts. Given these constraints from a remote client, say a laptop, it is possible to perform queries and have the results returned to the laptop provided the laptop has ssh access to the server. For the purpose of these examples the client computer is laptop.squeezel.com and the database computer is big.squeezel.com [chirico@laptop ~]$ ssh big.squeezel.com 'mysql -u user1 --password=s3cr3tpass45 --database=database1 -e "create table t1 (a int)"' Below the heading is removed -N and columns are tab separated. [chirico@laptop ~]$ ssh big.squeezel.com 'mysql -N -B -u user1 --password=s3cr3tpass45 --database=database1 -e "select * from t2"' A remote mysqldump is shown below. [chirico@laptop ~]$ ssh big.squeezel.com 'mysqldump -u user1 --password=s3cr3tpass45 --database=database1 t1' > localfile A perl example is shown below. Note the where clause below and the use of \\\" to escape quotes. (To download this example: wget http://downloads.sourceforge.net/souptonuts/perl_sshEx1.pl) #!/usr/bin/perl # Created by mchirico@users.sourceforge.net # Updated: Sat Jan 20 10:06:41 EST 2007 # perl_sshEx1.pl # # Download: http://downloads.sourceforge.net/souptonuts/perl_sshEx1.pl # # Shared keys must be setup on target server. # # # Put in Your Values Here. my $user="user1"; my $password="s3cr3tpass45"; my $database="database1"; my $remote_server="big.squeezel.com"; # my $SSH_CMD="ssh $remote_server 'mysql -N -B -u $user --database=$database --password=$password "; # # MySQL Command - Use \\\ for quotes. See below my $MySQL_CMD=" -e \"select * from email where name = \\\"Chirico\\\" \"'"; # # # open my $SCMD, "$SSH_CMD $MySQL_CMD|" or die "Could not ssh

"; while(<$SCMD>) { print $_; } # Files are closed automatically in Perl on exit, but # you can close if you like. close $SSH_CMD; LONGWINDED TIPS: LONGWINDED TIP 1: (May want to skip, since it's a long example) SQL Characteristic Functions: Do it without "if", "case", or "GROUP_CONCAT". Yes, there is use for this..."if" statements sometimes cause problems when used in combination. The simple secret, and it's also why they work in almost all databases, is the following functions: o sign (x) returns -1,0, +1 for values x < 0, x = 0, x > 0 respectively o abs( sign( x) ) returns 0 if x = 0 else, 1 if x > 0 or x < 0 o 1-abs( sign( x) ) complement of the above, since this returns 1 only if x = 0 Quick example: sign(-1) = -1, abs( sign(-1) ) = 1, 1-abs( sign(-1) ) = 0 Data for full example: CREATE TABLE exams ( pkey int(11) NOT NULL auto_increment, name varchar(15), exam int, score int, PRIMARY KEY (pkey) ); insert into exams (name,exam,score) values ('Bob',1,75); insert into exams (name,exam,score) values ('Bob',2,77); insert into exams (name,exam,score) values ('Bob',3,78); insert into exams (name,exam,score) values ('Bob',4,80); insert into exams (name,exam,score) values ('Sue',1,90); insert into exams (name,exam,score) values ('Sue',2,97); insert into exams (name,exam,score) values ('Sue',3,98); insert into exams (name,exam,score) values ('Sue',4,99); mysql> select * from exams; +------+------+------+-------+ | pkey | name | exam | score | +------+------+------+-------+ | 1 | Bob | 1 | 75 | | 2 | Bob | 2 | 77 | | 3 | Bob | 3 | 78 | | 4 | Bob | 4 | 80 | | 5 | Sue | 1 | 90 | | 6 | Sue | 2 | 97 | | 7 | Sue | 3 | 98 | | 8 | Sue | 4 | 99 | +------+------+------+-------+ 8 rows in set (0.00 sec) mysql> select name, sum(score*(1-abs(sign(exam-1)))) as exam1, sum(score*(1-abs(sign(exam-2)))) as exam2, sum(score*(1-abs(sign(exam-3)))) as exam3, sum(score*(1-abs(sign(exam-4)))) as exam4 from exams group by name; +------+-------+-------+-------+-------+ | name | exam1 | exam2 | exam3 | exam4 | +------+-------+-------+-------+-------+ | Bob | 75 | 77 | 78 | 80 | | Sue | 90 | 97 | 98 | 99 | +------+-------+-------+-------+-------+ 2 rows in set (0.00 sec) Note, the above pivot table was created with one select statement You may think IF's would be cleaner. NO, WATCH OUT! Look the following gives INCORRECT RESULTS! mysql> select name, if(exam=1,score,null) as exam1, if(exam=2,score,null) as exam2, if(exam=3,score,null) as exam3, if(exam=4,score,null) as exam4 from exams group by name; +------+-------+-------+-------+-------+ | name | exam1 | exam2 | exam3 | exam4 | +------+-------+-------+-------+-------+ | Bob | 75 | NULL | NULL | NULL | | Sue | 90 | NULL | NULL | NULL | +------+-------+-------+-------+-------+ 2 rows in set (0.00 sec) Note the above gives indeterminate results. Paul DuBois [ paul at snake.net ] showed me the correct way to perform this select statement. According to him When you include a GROUP BY clause in a query, the only values you can select are the grouped columns or summary values calculated from the groups. If you display additional columns, they're not tied to the grouped columns and the values displayed for them are indeterminate. If you rewrite the query like this, you get the correct result: select name, sum(if(exam=1,score,null)) as exam1, sum(if(exam=2,score,null)) as exam2, sum(if(exam=3,score,null)) as exam3, sum(if(exam=4,score,null)) as exam4 from exams group by name; +------+-------+-------+-------+-------+ | name | exam1 | exam2 | exam3 | exam4 | +------+-------+-------+-------+-------+ | Bob | 75 | 77 | 78 | 80 | | Sue | 90 | 97 | 98 | 99 | +------+-------+-------+-------+-------+ mysql> select name, sum(score*(1-abs(sign(exam-1)))) as exam1, sum(score*(1-abs(sign(exam-2)))) as exam2, sum(score*(1-abs(sign(exam-3)))) as exam3, sum(score*(1-abs(sign(exam-4)))) as exam4, sum(score*(1-abs(sign(exam- 2)))) - sum(score*(1-abs(sign(exam- 1)))) as delta_1_2, sum(score*(1-abs(sign(exam- 3)))) - sum(score*(1-abs(sign(exam- 2)))) as delta_2_3, sum(score*(1-abs(sign(exam- 4)))) - sum(score*(1-abs(sign(exam- 3)))) as delta_3_4 from exams group by name; +------+-------+-------+-------+-------+-----------+-----------+-----------+ | name | exam1 | exam2 | exam3 | exam4 | delta_1_2 | delta_2_3 | delta_3_4 | +------+-------+-------+-------+-------+-----------+-----------+-----------+ | Bob | 75 | 77 | 78 | 80 | 2 | 1 | 2 | | Sue | 90 | 97 | 98 | 99 | 7 | 1 | 1 | +------+-------+-------+-------+-------+-----------+-----------+-----------+ 2 rows in set (0.00 sec) Above delta_1_2 shows the difference between the first and second exams, with the numbers being positive because both Bob and Sue improved their score with each exam. Calculating the deltas here shows it's possible to compare two rows, not columns which is easily done with the standard SQL statements but rows in the original table. mysql>select name, sum(score*(1-abs(sign(exam-1)))) as exam1, sum(score*(1-abs(sign(exam-2)))) as exam2, sum(score*(1-abs(sign(exam-3)))) as exam3, sum(score*(1-abs(sign(exam-4)))) as exam4, sum(score*(1-abs(sign(exam- 2)))) - sum(score*(1-abs(sign(exam- 1)))) as delta_1_2, sum(score*(1-abs(sign(exam- 3)))) - sum(score*(1-abs(sign(exam- 2)))) as delta_2_3, sum(score*(1-abs(sign(exam- 4)))) - sum(score*(1-abs(sign(exam- 3)))) as delta_3_4, sum(score*(1-abs(sign(exam- 2)))) - sum(score*(1-abs(sign(exam- 1)))) + sum(score*(1-abs(sign(exam- 3)))) - sum(score*(1-abs(sign(exam- 2)))) + sum(score*(1-abs(sign(exam- 4)))) - sum(score*(1-abs(sign(exam- 3)))) as TotalIncPoints from exams group by name; +------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+ | name | exam1 | exam2 | exam3 | exam4 | delta_1_2 | delta_2_3 | delta_3_4 | TotalIncPoints | +------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+ | Bob | 75 | 77 | 78 | 80 | 2 | 1 | 2 | 5 | | Sue | 90 | 97 | 98 | 99 | 7 | 1 | 1 | 9 | +------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+ 2 rows in set (0.00 sec) TotalIncPoints shows the sum of the deltas. select name, sum(score*(1-abs(sign(exam-1)))) as exam1, sum(score*(1-abs(sign(exam-2)))) as exam2, sum(score*(1-abs(sign(exam-3)))) as exam3, sum(score*(1-abs(sign(exam-4)))) as exam4, sum(score*(1-abs(sign(exam- 2)))) - sum(score*(1-abs(sign(exam- 1)))) as delta_1_2, sum(score*(1-abs(sign(exam- 3)))) - sum(score*(1-abs(sign(exam- 2)))) as delta_2_3, sum(score*(1-abs(sign(exam- 4)))) - sum(score*(1-abs(sign(exam- 3)))) as delta_3_4, sum(score*(1-abs(sign(exam- 2)))) - sum(score*(1-abs(sign(exam- 1)))) + sum(score*(1-abs(sign(exam- 3)))) - sum(score*(1-abs(sign(exam- 2)))) + sum(score*(1-abs(sign(exam- 4)))) - sum(score*(1-abs(sign(exam- 3)))) as TotalIncPoints, (sum(score*(1-abs(sign(exam-1)))) + sum(score*(1-abs(sign(exam-2)))) + sum(score*(1-abs(sign(exam-3)))) + sum(score*(1-abs(sign(exam-4)))))/4 as AVG from exams group by name; +------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+-------+ | name | exam1 | exam2 | exam3 | exam4 | delta_1_2 | delta_2_3 | delta_3_4 | TotalIncPoints | AVG | +------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+-------+ | Bob | 75 | 77 | 78 | 80 | 2 | 1 | 2 | 5 | 77.50 | | Sue | 90 | 97 | 98 | 99 | 7 | 1 | 1 | 9 | 96.00 | +------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+-------+ 2 rows in set (0.00 sec) It's possible to combine Total Increasing Point TotalIncPoints with AVG. In fact, it's possible to combine all of the example cuts of the data into one SQL statement, which provides additional options for displaying data on your page select name, sum(score*(1-abs(sign(exam-1)))) as exam1, sum(score*(1-abs(sign(exam-2)))) as exam2, sum(score*(1-abs(sign(exam-3)))) as exam3, sum(score*(1-abs(sign(exam-4)))) as exam4, (sum(score*(1-abs(sign(exam-1)))) + sum(score*(1-abs(sign(exam-2)))))/2 as AVG1_2, (sum(score*(1-abs(sign(exam-2)))) + sum(score*(1-abs(sign(exam-3)))))/2 as AVG2_3, (sum(score*(1-abs(sign(exam-3)))) + sum(score*(1-abs(sign(exam-4)))))/2 as AVG3_4, (sum(score*(1-abs(sign(exam-1)))) + sum(score*(1-abs(sign(exam-2)))) + sum(score*(1-abs(sign(exam-3)))) + sum(score*(1-abs(sign(exam-4)))))/4 as AVG from exams group by name; +------+-------+-------+-------+-------+--------+--------+--------+-------+ | name | exam1 | exam2 | exam3 | exam4 | AVG1_2 | AVG2_3 | AVG3_4 | AVG | +------+-------+-------+-------+-------+--------+--------+--------+-------+ | Bob | 75 | 77 | 78 | 80 | 76.00 | 77.50 | 79.00 | 77.50 | | Sue | 90 | 97 | 98 | 99 | 93.50 | 97.50 | 98.50 | 96.00 | +------+-------+-------+-------+-------+--------+--------+--------+-------+ 2 rows in set (0.00 sec) Exam scores are listing along with moving averages...again it's all with one select statement. REFERENCES: Good article on Spatial Extensions with MySQL http://dev.mysql.com/tech-resources/articles/4.1/gis-with-mysql.html Good article on "Cross tabulations" or de-normalizing data to show stats: http://dev.mysql.com/tech-resources/articles/wizard/print_version.html MySQL performance tuning tips: http://www.linux-mag.com/cgi-bin/printer.pl?issue=2001-06&article=mysql See (TIP 26:) for links on normalization. Berkeley DB sample programs: Look for berkeleydb_0.0.24.tar.gz or the latest version at: http://sourceforge.net/project/showfiles.php?group_id=79066&package_id=80379 RECOMMENDED READING: "MySQL: The definitive guide to using, programming, and administering MySQL 4.1 and 5.0, Third Edition", Paul DuBois, Sams, Pub Date: March 08, 2005. ISBN: 978-0-672-32673-8 "MySQL Cookbook", Paul DuBois, O'Reilly, ISBN: 0-596-00145-2 "High Performance MySQL", Derek J. Balling, Jeremy Zawodny, ISBN: 0-596-00306-4 "Database Design for Mere Mortals", Michael J. Hernandez, Addison-Wesley "Securing MySQL: step-by-step",Artur Maj (See link below) http://www.securityfocus.com/infocus/1726

Other Tutorials Breaking Firewalls with OpenSSH and PuTTY: If the system administrator deliberately filters out all traffic except port 22 (ssh), to a single server, it is very likely that you can still gain access other computers behind the firewall. This article shows how remote Linux and Windows users can gain access to firewalled samba, mail, and http servers. In essence, it shows how openSSH and Putty can be used as a VPN solution for your home or workplace. Create a Live Linux CD - BusyBox and OpenSSH Included : These steps will show you how to create a functioning Linux system, with the latest 2.6 kernel compiled from source, and how to integrate the BusyBox utilities including the installation of DHCP. Plus, how to compile in the OpenSSH package on this CD based system. On system boot-up a filesystem will be created and the contents from the CD will be uncompressed and completely loaded into RAM -- the CD could be removed at this point for boot-up on a second computer. The remaining functioning system will have full ssh capabilities. You can take over any PC assuming, of course, you have configured the kernel with the appropriate drivers and the PC can boot from a CD. This tutorial steps you through the whole processes. SQLite Tutorial : This article explores the power and simplicity of sqlite3, first by starting with common commands and triggers, then the attach statement with the union operation is introduced in a way that allows multiple tables, in separate databases, to be combined as one virtual table, without the overhead of copying or moving data. Next, the simple sign function and the amazingly powerful trick of using this function in SQL select statements to solve complex queries with a single pass through the data is demonstrated, after making a brief mathematical case for how the sign function defines the absolute value and IF conditions. The Lemon Parser Tutorial: This article explains how to build grammars and programs using the lemon parser, which is faster than yacc. And, unlike yacc, it is thread safe. How to Compile the 2.6 kernel for Red Hat 9 and 8.0 and get Fedora Updates: This is a step by step tutorial on how to compile the 2.6 kernel from source. Linux System Admin Tips: There are over 160 linux tips and tricks in this article. This article is updated weekly. Virtual Filesystem: Building A Linux Filesystem From An Ordinary File. You can take a disk file, format it as ext2, ext3, or reiser filesystem and then mount it, just like a physical drive. Yes, it then possible to read and write files to this newly mounted device. You can also copy the complete filesystem, since it is just a file, to another computer. If security is an issue, read on. This article will show you how to encrypt the filesystem, and mount it with ACL (Access Control Lists), which give you rights beyond the traditional read (r) write (w) and execute (x) for the 3 user groups file, owner and other. Working With Time: What? There are 61 seconds in a minute? We can go back in time? We still tell time by the sun?

Mike Chirico, a father of triplets (all girls) lives outside of Philadelphia, PA, USA. He has worked with Linux since 1996, has a Masters in Computer Science and Mathematics from Villanova University, and has worked in computer-related jobs from Wall Street to the University of Pennsylvania. His hero is Paul Erdos, a brilliant number theorist who was known for his open collaboration with others.

Mike's notes page is souptonuts. For open source consulting needs, please send an email to mchirico@cwxstat.com. All consulting work must include a donation to SourceForge.net.



