Herman van Hovell f362363d14 [SPARK-14785] [SQL] Support correlated scalar subqueries ... ## What changes were proposed in this pull request? In this PR we add support for correlated scalar subqueries. An example of such a query is: ```SQL select * from tbl1 a where a.value > (select max(value) from tbl2 b where b.key = a.key) ``` The implementation adds the `RewriteCorrelatedScalarSubquery` rule to the Optimizer. This rule plans these subqueries using `LEFT OUTER` joins. It currently supports rewrites for `Project`, `Aggregate` & `Filter` logical plans. I could not find a well defined semantics for the use of scalar subqueries in an `Aggregate`. The current implementation currently evaluates the scalar subquery *before* aggregation. This means that you either have to make scalar subquery part of the grouping expression, or that you have to aggregate it further on. I am open to suggestions on this. The implementation currently forces the uniqueness of a scalar subquery by enforcing that it is aggregated and that the resulting column is wrapped in an `AggregateExpression`. ## How was this patch tested? Added tests to `SubquerySuite`. Author: Herman van Hovell <hvanhovell@questtec.nl> Closes #12822 from hvanhovell/SPARK-14785.		2016-05-02 16:32:31 -07:00
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src	[SPARK-14785] [SQL] Support correlated scalar subqueries	2016-05-02 16:32:31 -07:00
pom.xml	Revert "[SPARK-14613][ML] Add @Since into the matrix and vector classes in spark-mllib-local"	2016-04-28 19:57:41 -07:00