MDEV-38473 Incorrect Empty Set with HAVING clause when SELECT and GROUP BY use different aliases for the same column #4515
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…UP BY use different aliases for the same column MDEV-29300 fix causes a wrong result by incorrect removing a wrapper to an item that needed to be wrapped for the correct result. Direct access to the item causes an incorrect table reference to be used during join evaluation. We reverting that fix. Our original problem query is this SELECT (SELECT 0 GROUP BY c1 HAVING (SELECT c1)) FROM t1 group by c1; JOIN::prepare on /* select#2 */ select 0 group by t1.t1a having (subquery#3) fixing t1.t1a in group by clause, calls fix_outer_field() this item is resolved in an outer select (#1) and it is a grouping select, so we wrap it in Item_outer_ref and set this item to unfixed for later fixing in fix_inner_refs(). JOIN::prepare continues onto the having clause and fixes (subquery#3) which calls initiates the prepare series of calls, leading to setup_fields on the fields in this JOIN, one of which is an outer reference t1a. This is resolved to the item in the next most outer select in the group by clause. This item has been wrapped with an unfixed Item_outer_ref. It is found in resolve_ref_in_select_and_group() is it expected that this item will have already been fixed, hence this call in Item_field::fix_outer_field() DBUG_ASSERT(*ref && (*ref)->fixed()); but as explained above, it isn't fixed and debug builds assert here. Because this wrapper cannot be resolved here for reasons detailed in fix_inner_refs, and we cannot remove this wrapper without potentially returning an incorrect result, we have to relax this assertion.
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Pull request created in: https://jira.mariadb.org/browse/MDEV-38473