Incompatible Change: Prior to this release, when DATE values were compared with DATETIME values, the time portion of the DATETIME value was ignored, or the comparison could be performed as a string compare. Now a DATE value is coerced to the DATETIME type by adding the time portion as 00:00:00. To mimic the old behavior, use the CAST() function to cause the comparison operands to be treated as previously. For example: SELECT date_col = CAST(NOW() AS DATE);. (Bug#28929)

Incompatible Change: INSERT DELAYED is now downgraded to a normal INSERT if the statement uses functions that access tables or triggers, or that is called from a function or a trigger.

This was done to resolve the following interrelated issues:

(Bug#21483)

See also Bug#20497, Bug#21714

Security Fix: A malformed password packet in the connection protocol could cause the server to crash. Thanks for Dormando for reporting this bug, and for providing details and a proof of concept. (Bug#28984, CVE-2007-3780)

Security Fix: Use of a view could allow a user to gain update privileges for tables in other databases. (Bug#27878, CVE-2007-3782)

Security Fix: The requirement of the DROP privilege for RENAME TABLE was not enforced. (Bug#27515, CVE-2007-2691)

Security Fix: If a stored routine was declared using SQL SECURITY INVOKER, a user who invoked the routine could gain privileges. (Bug#27337, CVE-2007-2692)

Security Fix: CREATE TABLE LIKE did not require any privileges on the source table. Now it requires the SELECT privilege.

In addition, CREATE TABLE LIKE was not isolated from alteration by other connections, which resulted in various errors and incorrect binary log order when trying to execute concurrently a CREATE TABLE LIKE statement and either DDL statements on the source table or DML or DDL statements on the target table. (Bug#23667, Bug#25578, CVE-2007-3781)

Incompatible Change: When mysqldump was run with the --delete-master-logs option, binary log files were deleted before it was known that the dump had succeeded, not after. (The method for removing log files used RESET MASTER prior to the dump. This also reset the binary log sequence numbering to .000001.) Now mysqldump flushes the logs (which creates a new binary log number with the next sequence number), performs the dump, and then uses PURGE MASTER LOGS to remove the log files older than the new one. This also preserves log numbering because the new log with the next number is generated and only the preceding logs are removed. However, this may affect applications if they rely on the log numbering sequence being reset. (Bug#24733)

Incompatible Change: The use of an ORDER BY or DISTINCT clause with a query containing a call to the GROUP_CONCAT() function caused results from previous queries to be redisplayed in the current result. The fix for this includes replacing a BLOB value used internally for sorting with a VARCHAR. This means that for long results (more than 65,535 bytes), it is possible for truncation to occur; if so, an appropriate warning is issued. (Bug#23856, Bug#28273)