Incompatible Change: The parser accepted statements that contained /* ... */ that were not properly closed with */, such as SELECT 1 /* + 2. Statements that contain unclosed /*-comments now are rejected with a syntax error.

This fix has the potential to cause incompatibilities. Because of Bug#26302, which caused the trailing */ to be truncated from comments in views, stored routines, triggers, and events, it is possible that objects of those types may have been stored with definitions that now will be rejected as syntactically invalid. Such objects should be dropped and re-created so that their definitions do not contain truncated comments. If a stored object definition contains only a single statement (does not use a BEGIN ... END block) and contains a comment within the statement, the comment should be moved to follow the statement or the object should be rewritten to use a BEGIN ... END block. For example, this statement:

CREATE PROCEDURE p() SELECT 1 /* my comment */ ;

Can be rewritten in either of these ways:

CREATE PROCEDURE p() SELECT 1; /* my comment */
CREATE PROCEDURE p() BEGIN SELECT 1 /* my comment */ ; END;

(Bug#28779)

Security Fix: Using RENAME TABLE against a table with explicit DATA DIRECTORY and INDEX DIRECTORY options can be used to overwrite system table information by replacing the symbolic link points. the file to which the symlink points.

MySQL will now return an error when the file to which the symlink points already exists. (Bug#32111, CVE-2007-5969)

Incompatible Change: The file mysqld.exe was mistakenly included in binary distributions between MySQL 5.0.42 and 5.0.48. You should use mysqld-nt.exe. (Bug#32197)

Incompatible Change: Multiple-table DELETE statements containing ambiguous aliases could have unintended side effects such as deleting rows from the wrong table. Example:

DELETE FROM t1 AS a2 USING t1 AS a1 INNER JOIN t2 AS a2;

This bug fix enables alias declarations to be declared only in the table_references part. Elsewhere in the statement, alias references are allowed but not alias declarations. (Bug#30234)

See also Bug#27525.

Incompatible Change: Failure to consider collation when comparing space characters could result in incorrect index entry order, leading to incorrect comparisons, inability to find some index values, misordered index entries, misordered ORDER BY results, or tables that CHECK TABLE reports as having corrupt indexes.

As a result of this bug fix, indexes must be rebuilt for columns that use any of these character sets: eucjpms, euc_kr, gb2312, latin7, macce, ujis. See Checking Whether Tables or Indexes Must Be Rebuilt. (Bug#29461)