Fix incorrect handling of subquery pullup When pulling up a subquery, if the subquery's target list items are used in grouping set columns, we need to wrap them in PlaceHolderVars. This ensures that expressions retain their separate identity so that they will match grouping set columns when appropriate.
In 90947674f, we decided to wrap subquery outputs that are non-var expressions in PlaceHolderVars. This prevents const-simplification from merging them into the surrounding expressions after subquery pullup, which could otherwise lead to failing to match those subexpressions to grouping set columns, with the effect that they'd not go to null when expected. However, that left some loose ends. If the subquery's target list contains two or more identical Var expressions, we can still fail to match the Var expression to the expected grouping set expression. This is not related to const-simplification, but rather to how we match expressions to lower target items in setrefs.c. For sort/group expressions, we use ressortgroupref matching, which works well. For other expressions, we primarily rely on comparing the expressions to determine if they are the same. Therefore, we need a way to prevent setrefs.c from matching the expression to some other identical ones. To fix, wrap all subquery outputs in PlaceHolderVars if the parent query uses grouping sets, ensuring that they preserve their separate identity throughout the whole planning process. Reported-by: Dean Rasheed <dean.a.rash...@gmail.com> Author: Richard Guo <guofengli...@gmail.com> Reviewed-by: Dean Rasheed <dean.a.rash...@gmail.com> Discussion: https://postgr.es/m/cambws4-mesahaankskpbn0kkxdhaxc1_ejcvwhxeodqirrg...@mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/cc5d98525d43c22b98f360ef0f2c8d7dc57f04dc Modified Files -------------- src/backend/optimizer/prep/prepjointree.c | 93 ++++++++++++++++-------------- src/backend/rewrite/rewriteManip.c | 2 +- src/test/regress/expected/groupingsets.out | 29 ++++++++++ src/test/regress/sql/groupingsets.sql | 11 ++++ src/tools/pgindent/typedefs.list | 1 + 5 files changed, 93 insertions(+), 43 deletions(-)
