pingcap/tidb v4.0.15 on GitHub

Compatibility changes

Fix the issue that executing SHOW VARIABLES in a new session is slow. This fix reverts some changes made in #21045 and might cause compatibility issues. #24326

Fix a bug that collation is incorrectly set for binary literals when building range 26455
Fix the issue of wrong character set and collation for the case when expression #26671
Fix the "index out of range" error that occurs when a query includes both GROUP BY and UNION 26553
Fix the issue that TiDB might fail to send requests if TiKV has tombstone stores #25849
Fix the issue of unexpected behavior when casting the invalid string to DATE #27935
Fix the issue that column information is missed when converting the Apply operator to Join #27282
Fix a bug that the count distinct result on multiple columns is wrong when the new collation is enabled #27830
Fix the result wrong that occurs when the argument of the extract function is a negative duration #27236
Fix the wrong execution results that occur when the column in the group_concat function has a non-bin collation #27429
Fix the wrong execution results that occur when the collations around the between expression are different #27146
Fix the issue that greatest(datetime) union null returns empty string #26564
Fix the issue that the having clause might not work correctly #26496
Remove the undocumented /debug/sub-optimal-plan HTTP API #27264