release

As usual in this release, there are new SQL features, improvements to planning rules and Avatica, and lots of bug fixes. We’ll spotlight a couple of features make it easier to handle complex queries.

[CALCITE-816] allows you to represent sub-queries ( EXISTS , IN and scalar) as RexSubQuery, a kind of expression in the relational algebra. Until now, the sql-to-rel converter was burdened with expanding sub-queries, and people creating relational algebra directly (or via RelBuilder) could only create ‘flat’ relational expressions. Now we have planner rules to expand and de-correlate sub-queries.

Metadata is the fuel that powers query planning. It includes traditional query-planning statistics such as cost and row-count estimates, but also information such as which columns form unique keys, unique and what predicates are known to apply to a relational expression’s output rows. From the predicates we can deduce which columns are constant, and following [CALCITE-1023] we can now remove constant columns from GROUP BY keys.

Metadata is often computed recursively, and it is hard to safely and efficiently calculate metadata on a graph of RelNode s that is large, frequently cyclic, and constantly changing. [CALCITE-794] introduces a context to each metadata call. That context can detect cyclic metadata calls and produce a safe answer to the metadata request. It will also allow us to add finer-grained caching and further tune the metadata layer.

See the release notes; download the release.