Incompatible Change: InnoDB rolls back only the last statement on a transaction timeout. A new option, --innodb_rollback_on_timeout, causes InnoDB to abort and roll back the entire transaction if a transaction timeout occurs (the same behavior as in MySQL 5.0.13 and earlier). (Bug#24200)

Incompatible Change: The prepared_stmt_count system variable has been converted to the Prepared_stmt_count global status variable (viewable with the SHOW GLOBAL STATUS statement). (Bug#23159)

MySQL Cluster: Setting the configuration parameter LockPagesInMainMemory had no effect. (Bug#24461)

MySQL Cluster: It is now possible to create a unique hashed index on a column that is not defined as NOT NULL.

Unique indexes on columns in NDB tables do not store null values because they are mapped to primary keys in an internal index table (and primary keys cannot contain nulls).

Normally, an additional ordered index is created when one creates unique indexes on NDB table columns; this can be used to search for NULL values. However, if USING HASH is specified when such an index is created, no ordered index is created.

The reason for permitting unique hash indexes with null values is that, in some cases, the user wants to save space if a large number of records are pre-allocated but not fully initialized. This also assumes that the user will not try to search for null values. Since MySQL does not support indexes that are not allowed to be searched in some cases, the NDB storage engine uses a full table scan with pushed conditions for the referenced index columns to return the correct result.

A warning is returned if one creates a unique nullable hash index, since the query optimizer should be provided a hint not to use it with NULL values if this can be avoided. (Bug#21507)

DROP TRIGGER now supports an IF EXISTS clause. (Bug#23703)

The Com_create_user status variable was added (for counting CREATE USER statements). (Bug#22958)

The --memlock option relies on system calls that are unreliable on some operating systems. If a crash occurs, the server now checks whether --memlock was specified and if so issues some information about possible workarounds. (Bug#22860)

mysqldump now accepts the --debug-info option, which displays debugging information and memory and CPU usage statistics at program exit.

The bundled yaSSL library was upgraded to version 1.5.0.

MySQL Cluster: The failure of a data node failure during a schema operation could lead to additional node failures. (Bug#24752)

MySQL Cluster: A committed read could be attempted before a data node had time to connect, causing a timeout error. (Bug#24717)

MySQL Cluster: Sudden disconnection of an SQL or data node could lead to shutdown of data nodes with the error failed ndbrequire. (Bug#24447)

MySQL Cluster: ndb_config failed when trying to use 2 management servers and node IDs. (Bug#23887)

MySQL Cluster: If the value set for MaxNoOfAttributes is excessive, a suitable error message is now returned. (Bug#19352)

MySQL Cluster: A unique constraint violation was not ignored by an UPDATE IGNORE statement when the constraint violation occurred on a non-primary key. (Bug#18487, Bug#24303)

Cluster API: Using BIT values with any of the comparison methods of the NdbScanFilter class caused data nodes to fail. (Bug#24503)

Cluster API: Some MGM API function calls could yield incorrect return values in certain cases where the cluster was operating under a very high load, or experienced timeouts in inter-node communications. (Bug#24011)

The REPEAT() function could return NULL when passed a column for the count argument. (Bug#24947)

mysql_upgrade failed if the --password (or -p) option was given. (Bug#24896)

With innodb_file_per_table enabled, InnoDB displayed incorrect file times in the output from SHOW TABLE STATUS. (Bug#24712)

ALTER ENABLE KEYS or ALTER TABLE DISABLE KEYS combined with another ALTER TABLE option other than RENAME TO did nothing. In addition, if ALTER TABLE was used on a table having disabled keys, the keys of the resulting table were enabled. (Bug#24395)

The InnoDB mutex structure was simplified to reduce memory load. (Bug#24386)

The --extern option for mysql-test-run.pl did not function correctly. (Bug#24354)

Foreign key identifiers for InnoDB tables could not contain certain characters. (Bug#24299)

The mysql.server script used the source command, which is less portable than the . command; it now uses . instead. (Bug#24294)

ALTER TABLE statements that performed both RENAME TO and {ENABLE|DISABLE} KEYS operations caused a server crash. (Bug#24219)

The loose index scan optimization for GROUP BY with MIN or MAX was not applied within other queries, such as CREATE TABLE ... SELECT ..., INSERT ... SELECT ..., or in the FROM clauses of subqueries. (Bug#24156)

Subqueries for which a pushed-down condition did not produce exactly one key field could cause a server crash. (Bug#24056)

The size of MEMORY tables and internal temporary tables was limited to 4GB on 64-bit Windows systems. (Bug#24052)

ROW_COUNT() did not work properly as an argument to a stored procedure. (Bug#23760)

LAST_DAY('0000-00-00') could cause a server crash. (Bug#23653)

A trigger that invoked a stored function could cause a server crash when activated by different client connections. (Bug#23651)

The stack size for NetWare binaries was increased to 128KB to prevent problems caused by insufficient stack size. (Bug#23504)

If elements in a non-top-level IN subquery were accessed by an index and the subquery result set included a NULL value, the quantified predicate that contained the subquery was evaluated to NULL when it should return a non-NULL value. (Bug#23478)

When applying the group_concat_max_len limit, GROUP_CONCAT() could truncate multi-byte characters in the middle. (Bug#23451)

mysql_affected_rows() could return values different from mysql_stmt_affected_rows() for the same sequence of statements. (Bug#23383)

Accuracy was improved for comparisons between DECIMAL columns and numbers represented as strings. (Bug#23260)

Calculation of COUNT(DISTINCT), AVG(DISTINCT), or SUM(DISTINCT) when they are referenced more than once in a single query with GROUP BY could cause a server crash. (Bug#23184)

Changes to character set variables prior to an action on a replication-ignored table were forgotten by slave servers. (Bug#22877)

Queries using a column alias in an expression as part of an ORDER BY clause failed, an example of such a query being SELECT mycol + 1 AS mynum FROM mytable ORDER BY 30 - mynum. (Bug#22457)

Using EXPLAIN caused a server crash for queries that selected from INFORMATION_SCHEMA in a subquery in the FROM clause. (Bug#22413)

A server crash occurred when using LOAD DATA to load a table containing a NOT NULL spatial column, when the statement did not load the spatial column. Now a NULL supplied to NOT NULL column error occurs. (Bug#22372)

DATE_ADD() requires complete dates with no “zero” parts, but sometimes did not return NULL when given such a date. (Bug#22229)

Some small double precision numbers (such as 1.00000001e-300) that should have been accepted were truncated to zero. (Bug#22129)

For a nonexistent table, DROP TEMPORARY TABLE failed with an incorrect error message if read_only was enabled. (Bug#22077)

Trailing spaces were not removed from Unicode CHAR column values when used in indexes. This resulted in excessive usage of storage space, and could affect the results of some ORDER BY queries that made use of such indexes.

(Bug#22052)

STR_TO_DATE() returned NULL if the format string contained a space following a non-format character. (Bug#22029)

In some cases, the parser failed to distinguish a user-defined function from a stored function. (Bug#21809)

Inserting a default or invalid value into a spatial column could fail with Unknown error rather than a more appropriate error. (Bug#21790)

It was possible to use DATETIME values whose year, month, and day parts were all zeroes but whose hour, minute, and second parts contained nonzero values, an example of such an illegal DATETIME being '0000-00-00 11:23:45'.

(Bug#21789)

See also Bug#25301

yaSSL crashed on pre-Pentium Intel CPUs. (Bug#21765)

Evaluation of subqueries that require the filesort algorithm were allocating and freeing the sort_buffer_size buffer many times, resulting in slow performance. Now the buffer is allocated once and reused. (Bug#21727)

Through the C API, the member strings in MYSQL_FIELD for a query that contains expressions may return incorrect results. (Bug#21635)

Using FLUSH TABLES in one connection while another connection is using HANDLER statements caused a server crash.

(Bug#21587)

See also Bug#29474

View columns were always handled as having implicit derivation, leading to illegal mix of collation errors for some views in UNION operations. Now view column derivation comes from the original expression given in the view definition. (Bug#21505)

InnoDB crashed while performing XA recovery of prepared transactions. (Bug#21468)

INET_ATON() returned a signed BIGINT value, not an unsigned value. (Bug#21466)

It was possible to set the backslash character (“ \ ”) as the delimiter character using DELIMITER, but not actually possible to use it as the delimiter. (Bug#21412)

Selecting into variables sometimes returned incorrect wrong results. (Bug#20836)

On slave servers, transactions that exceeded the lock wait timeout failed to roll back properly. (Bug#20697)

CONCURRENT did not work correctly for LOAD DATA INFILE. (Bug#20637)

mysql_fix_privilege_tables.sql altered the table_privs.table_priv column to contain too few privileges, causing loss of the CREATE VIEW and SHOW VIEW privileges. (Bug#20589)

With lower_case_table_names set to 1, SHOW CREATE TABLE printed incorrect output for table names containing Turkish I (LATIN CAPITAL LETTER I WITH DOT ABOVE). (Bug#20404)

A query with a subquery that references columns of a view from the outer SELECT could return an incorrect result if used from a prepared statement. (Bug#20327)

For queries that select from a view, the server was returning MYSQL_FIELD metadata inconsistently for view names and table names. For view columns, the server now returns the view name in the table field and, if the column selects from an underlying table, the table name in the org_table field. (Bug#20191)

Invalidating the query cache caused a server crash for INSERT INTO ... SELECT statements that selected from a view. (Bug#20045)

Unsigned BIGINT values treated as signed values by the MOD() function. (Bug#19955)

Compiling PHP 5.1 with the MySQL static libraries failed on some versions of Linux. (Bug#19817)

The DELIMITER statement did not work correctly when used in an SQL file run using the SOURCE statement. (Bug#19799)

For a cast of a DATETIME value containing microseconds to DECIMAL, the microseconds part was truncated without generating a warning. Now the microseconds part is preserved. (Bug#19491)

SQL statements close to the size of max_allowed_packet could produce binary log events larger than max_allowed_packet that could not be read by slave servers. (Bug#19402)

VARBINARY column values inserted on a MySQL 4.1 server had trailing zeroes following upgrade to MySQL 5.0 or later. (Bug#19371)

The server could send incorrect column count information to the client for queries that produce a larger number of columns than can fit in a two-byte number. (Bug#19216)

For some problems relating to character set conversion or incorrect string values for INSERT or UPDATE, the server was reporting truncation or length errors instead. (Bug#18908)

Constant expressions and some numeric constants used as input parameters to user-defined functions were not treated as constants. (Bug#18761)

myisampack wrote to unallocated memory, causing a crash. (Bug#17951)

FLUSH LOGS or mysqladmin flush-logs caused a server crash if the binary log was not open. (Bug#17733)

mysql_fix_privilege_tables did not handle a password containing embedded space or apostrophe characters. (Bug#17700)

Attempting to use a view containing DEFINER information for a non-existent user resulted in an error message that revealed the definer account. Now the definer is revealed only to superusers. Other users receive only an access denied message. (Bug#17254)

IN() and CHAR() can return NULL, but did not signal that to the query processor, causing incorrect results for IS NULL operations. (Bug#17047)

Slave servers would retry the execution of a SQL statement an infinite number of times, ignoring the value SLAVE_TRANSACTION_RETRIES when using the NDB engine. (Bug#16228)

Warnings were generated when explicitly casting a character to a number (for example, CAST('x' AS SIGNED)), but not for implicit conversions in simple arithmetic operations (such as 'x' + 0). Now warnings are generated in all cases. (Bug#11927)

Metadata for columns calculated from scalar subqueries was limited to integer, double, or string, even if the actual type of the column was different. (Bug#11032)

Subqueries of the form NULL IN (SELECT ...) returned invalid results. (Bug#8804, Bug#23485)