Incompatible Change: An additional correction to the original MySQL 5.1.23 fix was made to normalize directory names before adding them to the list of directories. This prevents /etc/ and /etc from being considered different, for example. (Bug#20748)

See also Bug#38180

Partitioning: A LIST partitioned MyISAM table returned erroneous results when an index was present on a column in the WHERE clause and NOT IN was used on that column.

Searches using the index were also much slower then if the index were not present. (Bug#35931)

Partitioning: SELECT COUNT(*) was not correct for some partitioned tables using a storage engine that did not support HA_STATS_RECORDS_IS_EXACT. Tables using the ARCHIVE storage engine were known to be affected.

This was because ha_partition::records() was not implemented, and so the default handler::records() was used in its place. However, this is not correct behavior if the storage engine does not support HA_STATS_RECORDS_IS_EXACT.

The solution was to implement ha_partition::records() as a wrapper around the underlying partition records.

As a result of this fix, the rows column in the output of EXPLAIN PARTITIONS now includes the total number of records in the partitioned table. (Bug#35745)

Replication: Some kinds of internal errors (such as Out of stack) cuased the server to crash. (Bug#37150)

Replication: Row-based replication did not correctly copy TIMESTAMP values from a big-endian storage engine to a little-endian storage engine. (Bug#37076)

Server-side cursors were not initialized properly, which could cause a server crash. (Bug#38486)

The fix for Bug#20748 caused a problem such that on Unix, MySQL programs looked for options in ~/my.cnf rather than the standard location of ~/.my.cnf. (Bug#38180)

If the table definition cache contained tables with many BLOB columns, much memory could be allocated to caching BLOB values. Now a size limit on the cached BLOB values is enforced. (Bug#38002)

For InnoDB tables, ORDER BY ... DESC sometimes returned results in ascending order. (Bug#37830)

The server returned unexpected results if a right side of the NOT IN clause consisted of the NULL value and some constants of the same type. For example, this query might return 3, 4, 5, and so forth if a table contained those values:

SELECT * FROM t WHERE NOT t.id IN (NULL, 1, 2);

(Bug#37761)

Setting the session value of the innodb_table_locks system variable caused a server crash. (Bug#37669)

Nesting of IF() inside of SUM() could cause an extreme server slowdown. (Bug#37662)

Killing a query that used an EXISTS subquery as the argument to SUM() or AVG() caused a server crash. (Bug#37627)

SELECT DISTINCT from a simple view on an InnoDB table, where all selected columns belong to the same unique index key, returned incorrect results. (Bug#36632)

The mysql client failed to recognize comment lines consisting of -- followed by a newline. (Bug#36244)

The UUID() function returned UUIDs with the wrong time; this was because the offset for the time part in UUIDs was miscalculated. (Bug#35848)

The configure script did not allow utf8_hungarian_ci to be specified as the default collation. (Bug#35808)

Freeing of an internal parser stack during parsing of complex stored programs caused a server crash. (Bug#35577, Bug#37269, Bug#37728)

mysqlbinlog left temporary files on the disk after shutdown, leading to the pollution of the temporary directory, which eventually caused mysqlbinlog to fail. This caused problems in testing and other situations where mysqlbinlog might be invoked many times in a relatively short period of time. (Bug#35543)

Index scans performed with the sort_union() access method returned bad data when the sort_buffer_size limit was reached. (Bug#35478)

A significant slowdown occurred when many SELECT statements that return many rows from InnoDB tables were running concurrently. (Bug#34409)

mysql_install_db failed if the server was running with a SQL mode of TRADITIONAL. This program now resets the SQL mode internally to avoid this problem. (Bug#34159)

Fast ALTER TABLE operations were not fast for columns that used multibyte character sets. (Bug#33873)

The internal functions my_getsystime(), my_micro_time(), and my_micro_time_and_time() did not work correctly on Windows. One symptom was that uniqueness of UUID() values could be compromised. (Bug#33748)

Cached queries that used 256 or more tables were not properly cached, so that later query invalidation due to a TRUNCATE TABLE for one of the tables caused the server to hang. (Bug#33362)

mysql_upgrade attempted to use the /proc filesystem even on systems that do not have it. (Bug#31605)

The Serbian translation for the ER_INCORRECT_GLOBAL_LOCAL_VAR error was corrected. (Bug#29738)

In some cases, the parser interpreted the ; character as the end of input and misinterpreted stored program definitions. (Bug#26030)

The FLUSH PRIVILEGES statement did not produce an error when it failed. (Bug#21226)

After executing a prepared statement that accesses a stored function, the next execution would fail to find the function if the stored function cache was flushed in the meantime. (Bug#12093, Bug#21294)