mirror of https://github.com/apache/druid.git
d4cace385f
* SQL: Allow Scans to be used as outer queries. This has been possible in the native query system for a while, but the capability hasn't yet propagated into the SQL layer. One example of where this is useful is a query like: SELECT * FROM (... LIMIT X) WHERE <filter> Because this expands the kinds of subquery structures the SQL layer will consider, it was also necessary to improve the cost calculations. These changes appear in PartialDruidQuery and DruidOuterQueryRel. The ideas are: - Attach per-column penalties to the output signature of each query, instead of to the initial projection that starts a query. This encourages moving projections into subqueries instead of leaving them on outer queries. - Only attach penalties to projections if there are actually expressions happening. So, now, projections that simply reorder or remove fields are free. - Attach a constant penalty to every outer query. This discourages creating them when they are not needed. The changes are generally beneficial to the test cases we have in CalciteQueryTest. Most plans are unchanged, or are changed in purely cosmetic ways. Two have changed for the better: - testUsingSubqueryWithLimit now returns a constant from the subquery, instead of returning every column. - testJoinOuterGroupByAndSubqueryHasLimit returns a minimal set of columns from the innermost subquery; two unnecessary columns are no longer there. * Fix various DS operator conversions. These were all implemented as direct conversions, which isn't appropriate because they do not actually map onto native functions. These are only usable as post-aggregations. * Test case adjustment. |
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