Compatibility changes

• Make the SHOW DATABASES LIKE … statement case-insensitive #34766 @e1ijah1
• Change the default value of tidb_enable_outer_join_reorder from 1 to 0, which disables Join Reorder's support for Outer Join by default.

Improvements

• Add a new optimizer SEMI_JOIN_REWRITE to improve the performance of EXISTS queries #35323 @winoros

Bug fixes

• Fix the issue that INL_HASH_JOIN might hang when used with LIMIT #35638 @guo-shaoge
• Fix the issue that TiDB might panic when executing the UPDATE statement #32311 @Yisaer
• Fix a bug that TiDB might send coprocessor requests when executing the SHOW COLUMNS statement #36496 @tangenta
• Fix a bug that TiDB might return the invalid memory address or nil pointer dereference error when executing the SHOW WARNINGS statement #31569 @zyguan
• Fix a bug that in the static partition prune mode, SQL statements with an aggregate condition might return wrong result when the table is empty #35295 @tiancaiamao
• Fix the issue that the Join Reorder operation will mistakenly push down its Outer Join condition #37238 @winoros
• Fix the issue that CTE-schema hash code is cloned mistakenly, which causes the Can't find column ... in schema ... error when CTE is referenced more than once #35404 @AilinKid
• Fix the issue that the wrong join reorder in some right outer join scenarios causes wrong query result #36912 @winoros
• Fix the issue of incorrectly inferred null flag of the TiFlash firstrow aggregate function in the EqualAll case #34584 @fixdb
• Fix the issue that Plan Cache does not work when a binding is created with the IGNORE_PLAN_CACHE hint #34596 @fzzf678
• Fix the issu that an EXCHANGE operator is missing between the hash-partition window and the single-partition window #35990 @LittleFall
• Fix the issue that partitioned tables cannot fully use indexes to scan data in some cases #33966 @mjonss
• Fix the issue of wrong query result when a wrong default value is set for partial aggregation after the aggregation is pushed down #35295 @tiancaiamao
• Fix the issue that querying partitioned tables might get the index-out-of-range error in some cases #35181 @mjonss
• Fix the issue that a partition is incorrectly pruned if a partition key is used in the query condition and the collate is different from the one in the query partition table #32749 @mjonss
• Fix the issue that when TiDB Binlog is enabled, executing the ALTER SEQUENCE statement might cause a wrong metadata version and cause Drainer to exit #36276 @AilinKid
• Fix the issue of incorrect TiDB status that might appear on startup in some extreme cases #36791 @xhebox
• Fix the potential UnknownPlanID issue that occurs when querying the execution plans for partitioned tables in TiDB Dashboard #35153 @time-and-fate
• Fix the issue that the column list does not work in the LOAD DATA statement #35198 @SpadeA-Tang
• Fix the issue of the data and columnID count not match error that occurs when inserting duplicated values with TiDB Binlog enabled #33608 @zyguan
• Remove the limitation of tidb_gc_life_time #35392 @TonsnakeLin
• Fix the LOAD DATA statement dead loop when an empty filed terminator is used #33298 @zyguan
• Avoid sending requests to unhealthy TiKV nodes to improve availability #34906 @sticnarf