SQL : Variations on Insert statement and Interview Questions.









Variation on INSERT statement:

There are three variations of insert statement as shown below:

1. Changing the order of the columns:

You can change the order of the column names as long as the matching values for each column come in that same order.

Example: We previously use this method:

INSERT INTO stu_data(student_name, student_rollno, student_mobileno) VALUES ('ABC', 1, 8945372531);

We also use this method for inserting the data:





INSERT INTO stu_data(student_rollno, student_mobileno, student_name) VALUES (2, 8945372531, 'ABD');





In this method we change the order and matching values of the columns.



2. Omitting columns name:

If you want to enter the data in all values then you have no need to write the columns name but the data must be in the same order as you inserted the column name.

Example: INSERT INTO stu_data VALUES ('BCD', 3, 7654321987);











3. Leaving some column out :

You can also insert few columns like

INSERT INTO stu_data(student_rollno) VALUES (4);



And if you want to insert the remaining data then you can insert by applying 'where' clause with 'INSERT' , which we understood later.





INTERVIEW QUESTIONS:





1. What are the subsets of SQL.

The subset of SQL are:

1. Data Definition Language (DDL).



2. Data Manipulation Language (DML).



3. Data Control Language (DCL).



DDL: Allows you to define the structure of the database.



Common DDL commands are: CREATE, DROP, ALTER,

DESCRIBE, TRUNCATE.



Common DML commands are: SELECT, INSERT, UPDATE, DELETE.





Common DCL commands are: GRANT, REVOKE.









2.

Explain DDL commands.





CREATE Command: It is used to create the structure of the table inside the database.

SYNTAX: CREATE TABLE table_name(col_1 datatype, col_2 datatype,.......col_N datatype);



DESCRIBE Command: It is used to describe or see the structure of table.

SYNTAX: DESC table_name;



DROP Command: It is used to drop the data with structure of table.

SYNTAX: DROP table_name;



TRUNCATE Command: It is used to delete the records permanently from the database and free the space containing the table.

SYNTAX: TRUNCATE TABLE table_name;



ALTER Command: It is used to do changes in the structure of the table.

SYNTAX: ALTER TABLE table_name ADD(col_1 datatype);

ALTER TABLE table_name MODIFY(col_1 datatype);





3. Explain DML Commands.





SELECT Command: It is used to see the records present in the database.

SYNTAX: SELECT * FROM table_name;

SELECT col_1,col_2 FROM table_name;

INSERT Command: It is used to insert the record in the database.

SYNTAX: As given above.

UPDATE Command: It is used to change or update the records into the database.

SYNTAX: UPDATE table_name set col_x=value WHERE condition;

DELETE Command: It is used to delete or remove the records into the database temporarily.

SYNTAX: DELETE FROM table_name;

DELETE FROM table_name WHERE expression;

3. Explain DCL Commands.





GRANT Command: It is used to give privileges to database.

SYNTAX: GRANT CREATE TABLE to username;

REVOKE Command: It is used to take back privileges from user.

SYNTAX: REVOKE CREATE TABLE to username;

We will discuss about all these command later in brief.













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