1f91c8ca1d
examine_simple_variable supposed that any RTE_SUBQUERY rel it gets pointed at must have been planned already. However, this isn't a safe assumption because we must do selectivity estimation while generating indexscan paths, and that code might look at join clauses involving a rel that the loop in set_base_rel_sizes() hasn't reached yet. The simplest fix is to play dumb in such a situation, that is give up trying to extract any stats for the Var. This could possibly be improved by making a separate pass over the RTE list to plan each unflattened subquery before we start the main planning work --- but that would be pretty invasive and it doesn't seem worth it, for now at least. (We couldn't just break set_base_rel_sizes() into two loops: the prescan would need to handle all subquery rels in the query, not only those in the current join subproblem.) This bug was introduced in commit 1cb108efb0e60d87e4adec38e7636b6e8efbeb57, although I think that subsequent changes may have exposed it more than it was originally. Per bug #7580 from Maxim Boguk.
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