Add correlated columns to LogicalDistinct::distinct_targets when flattening dependent joins #5286
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Since the pipeline rework in #4970 we can now execute
UNIONpipelines in parallel. This uncovered an issue with our correlated subquery flattening, which very rarely showed up in our CI. It seemed like a race condition, but it was not!When creating the physical plan for a
LogicalDistinct, we created afirstaggregate for every non-group column. This usually worked, but this aggregate is order-dependent. If theLogicalDistinctis the sink of one or more union pipelines, the input order is no longer guaranteed, since these are now executed in parallel.The solution is to add the correlated column to the
distinct_targets, so that it is a group, rather than afirstaggregate.