Incompatible Change: Client authentication now is based on 41-byte passwords in the user table, not 45-byte passwords as in 4.1.0. Any 45-byte passwords created for 4.1.0 must be reset after running the mysql_fix_privilege_tables script.

Incompatible Change: Renamed the C API mysql_prepare_result() function to mysql_get_metadata() because the old name was confusing.

Replication: ANALYZE TABLE, OPTIMIZE TABLE, REPAIR TABLE, and FLUSH statements are now stored in the binary log and thus replicated to slaves. This logging does not occur if the optional NO_WRITE_TO_BINLOG keyword (or its alias LOCAL) is given. Exceptions are that FLUSH LOGS, FLUSH MASTER, FLUSH SLAVE, and FLUSH TABLES WITH READ LOCK are not logged in any case. For a syntax example, see Section 12.4.6.2, “FLUSH Syntax”.

Replication: Replication over SSL now works.

The --old-protocol option for mysqld is no longer supported and has been removed.

When using SET sql_mode='mode' for a complex mode (such as ANSI), we now update the sql_mode variable to include all the individual options implied by the complex mode.

CHAR, VARCHAR, and TEXT columns now have lengths measured in characters rather than in bytes. The character size depends on the column's character set. This means, for example, that a CHAR(n) column for a multi-byte character set takes more storage than before. Similarly, index values on such columns are measured in characters, not bytes.

Renamed CLIENT_MULTI_QUERIES connect option flag to CLIENT_MULTI_STATEMENTS. To allow for a transition period, the old option continues to be recognized for a while.

Added --secure-auth option to mysql command-line client. If this option is set, the client refuses to send passwords in old (pre-4.1.1) format.

The mysql_next_result() C API function now returns -1 if there are no more result sets.

It is now possible to create multiple key caches, assign table indexes to particular caches, and to preload indexes into caches. See Section 12.4.6.1, “CACHE INDEX Syntax”. See Section 12.4.6.4, “LOAD INDEX INTO CACHE Syntax”. Structured system variables are introduced as a means of grouping related key cache parameters. See Section 5.1.5.1, “Structured System Variables”.

Added SHOW BDB LOGS as an alias for SHOW LOGS.

Added character_set_client, character_set_connection, character_set_database, character_set_results, character_set_server, character_set_system, collation_connection, collation_database, and collation_server system variables to provide information about character sets and collations.

The DATABASE() function now returns NULL rather than the empty string if there is no database selected.

Removed unused ft_max_word_len_for_sort variable from myisamchk.

Removed unused ft_max_word_len_for_sort system variable.

Added aggregate function BIT_XOR() for bitwise XOR operations.

The --lower-case-table-names=1 server option now also makes aliases case insensitive. (Bug#534)

Require DEFAULT before table and database default character set. This enables us to use ALTER TABLE tbl_name ... CHARACTER SET=... to change the character set for all CHAR, VARCHAR, and TEXT columns in a table.

Added --sql-mode=NO_AUTO_VALUE_ON_ZERO option to suppress the usual behavior of generating the next sequence number when zero is stored in an AUTO_INCREMENT column. With this mode enabled, zero is stored as zero; only storing NULL generates a sequence number.

Added SHOW MASTER LOGS as an alias for SHOW BINARY LOGS. (In 4.1.0, SHOW MASTER LOGS was renamed to SHOW BINARY LOGS. Now you can use either one.)

Full-text search now supports multi-byte character sets and the Unicode utf8 character set. (The Unicode ucs2 character set is not yet supported.)

EXPLAIN now supports an EXTENDED option. When given, EXPLAIN generates extra information that may be viewed with the SHOW WARNINGS statement.

Added IGNORE option for DELETE statement.

Added mysql_sqlstate() and mysql_stmt_sqlstate() C API client functions that return the SQLSTATE error code for the last error.

Renamed bdb_version system variable to version_bdb.

LOAD DATA now produces warnings that can be fetched with SHOW WARNINGS.

Added support for syntax CREATE TABLE table2 (LIKE table1) that creates an empty table table2 with a definition that is exactly the same as table1, including any indexes.

The START SLAVE statement now supports an UNTIL clause for specifying that the slave SQL thread should be started but run only until it reaches a given position in the master's binary logs or in the slave's relay logs.

Most subqueries are now much faster than before.

MySQL source distributions now also include the MySQL Internals Manual internals.texi.

Added Slave_IO_State and Seconds_Behind_Master columns to the output of SHOW SLAVE STATUS. Slave_IO_State indicates the state of the slave I/O thread, and Seconds_Behind_Master indicates the number of seconds by which the slave is late compared to the master.

Added mysql_set_server_option() C API client function to allow multiple statement handling in the server to be enabled or disabled.

Added MATCH ... AGAINST( ... WITH QUERY EXPANSION) and the ft_query_expansion_limit system variable.

The interface to aggregate user-defined functions has changed a bit. You must now declare a xxx_clear() function for each aggregate function XXX(). xxx_clear() is used instead of xxx_reset().

Added preload_buffer_size system variable.

Added delimiter (\d) command to the mysql command-line client for changing the statement delimiter (terminator). The default delimiter is semicolon.

mysqldump now includes a statement in the dump output to set foreign_key_checks to 0 to avoid problems with tables having to be reloaded in a particular order when the dump is reloaded. The existing foreign_key_checks value is saved and restored.

Phrase search in MATCH ... AGAINST ( ... IN BOOLEAN MODE) no longer matches partial words.

Added new %f microseconds format specifier for DATE_FORMAT() and TIME_FORMAT().

Added secure_auth global server system variable and --secure-auth server option that disallow authentication for accounts that have old (pre-4.1.1) passwords.

Changed that the relay log is flushed to disk by the slave I/O thread every time it reads a relay log event. This reduces the risk of losing some part of the relay log in case of brutal crash.

Table aliases are not case sensitive if lower_case_table_names is nonzero.

The --quote-names option for mysqldump now is enabled by default.

Produce warnings even for single-row INSERT statements, not just for multiple-row INSERT statements. Previously, it was necessary to set sql_warnings = 1 to generate warnings for single-row statements.

Added PURGE BINARY LOGS as an alias for PURGE MASTER LOGS.

MyISAM tables now use a better checksum algorithm (if checksum is enabled with CREATE TABLE ... CHECKSUM = 1). Old tables will appear to have incorrect checksum, and should be repaired.

All queries in which at least one SELECT does not use indexes properly now are written to the slow query log when long log format is used.

It is now possible to create a MERGE table from MyISAM tables in different databases. Formerly, all the MyISAM tables had to be in the same database, and the MERGE table had to be created in that database as well.

Added new ADDTIME(), DATE(), DATEDIFF(), LAST_DAY(), MAKEDATE(), MAKETIME(), MICROSECOND(), SUBTIME(), TIME(), TIMEDIFF(), TIMESTAMP(), UTC_DATE(), UTC_TIME(), UTC_TIMESTAMP(), and WEEKOFYEAR() functions.

CREATE TABLE tbl_name (...) TYPE=storage_engine now generates a warning if the named storage engine is not available. The table is still created as a MyISAM table, as before.

New global system variable relay_log_purge to enable or disable automatic relay log purging.

Added new COMPRESS(), UNCOMPRESS(), and UNCOMPRESSED_LENGTH() functions.

Added DROP USER 'user_name'@'host_name' statement to drop an account that has no privileges.

New COERCIBILITY() function to return the collation coercibility of a string.

LIMIT no longer accepts negative arguments (they used to be treated as very big positive numbers before).

You can revoke all privileges from a user with REVOKE ALL PRIVILEGES, GRANT FROM user_list.

Added the OLAP (On-Line Analytical Processing) function ROLLUP, which provides summary rows for each GROUP BY level.

Disabled the PURGE LOGS statement that was added in version 4.1.0. The statement now should be issued as PURGE MASTER LOGS or PURGE BINARY LOGS.

Added new syntax for ADDDATE() and SUBDATE(). The second argument now may be a number representing the number of days to be added to or subtracted from the first date argument.

TIME columns with hour values greater than 24 were returned incorrectly to the client.

Added new type values DAY_MICROSECOND, HOUR_MICROSECOND, MINUTE_MICROSECOND, SECOND_MICROSECOND, and MICROSECOND for DATE_ADD(), DATE_SUB(), and EXTRACT().

New CHECKSUM TABLE statement for reporting table checksum values.

Added SQLSTATE codes for all server errors.

Security Fix: Connections from some IP addresses were assigned incorrect database-level privileges. A connection could be assigned the database privileges of the previous successful authentication from one of those IP addresses, even if the IP address user name and database name were different. (Bug#1636)

Security Fix: A server compiled without SSL support still allowed connections by users who had the REQUIRE SSL option specified for their accounts.

Replication: When an undefined user variable was used in a updating query on the master (such as INSERT INTO t VALUES(@a), where @a had never been set by this connection before), the slave could replicate the query incorrectly if a previous transaction on the master used a user variable of the same name. (Bug#1331)

Replication: The new PASSWORD() function in 4.1 is now properly replicated. (Bug#344)

Replication: Replication failed between a 3.23 master and a 4.0 slave. The slave lost replicated temporary tables if FLUSH LOGS was issued on the master. (Bug#254)

Replication: CONNECTION_ID() now is properly replicated. (Bug#177)

Replication: When a transaction spanned two or more relay logs, and the slave was stopped while executing the part of the transaction that was in the second or later relay log, replication resumed at the beginning of the second or later relay log, which was incorrect. (It should resume at BEGIN, in the first relay log.) (Bug#53)

Privileges could be escalation via database wildcards in GRANT statements. (Bug#3924)

When ALTER TABLE RENAME, was used to rename a table with the same name in another database, it silently dropped the destination table if it existed. (Bug#2628)

SLAVE START (which is a deprecated syntax, START SLAVE should be used instead) could crash the slave. (Bug#2516)

Following a call to mysql_prepare(), placeholders were allowed in all consequent statements, even if they were not prepared. (Bug#1946)

Using the ? prepared statement parameter as the argument to certain functions or statement clauses caused a server crash when mysql_prepare() was invoked. (Bug#1500)

Name resolution of columns of reduced subqueries in UNION statements was not always performed correctly. (Bug#745)

A memory overrun could occur due to in subqueries in the SELECT list with WHERE clause larger than that of the outer query's WHERE clause. (Bug#726)

HASH, BTREE, RTREE, ERRORS, and WARNINGS no longer are reserved words. (Bug#724)

ROLLUP did not work correctly when all tables in the join were const tables. (Bug#714)

A problem with UNION kept NULL values from being inserted into result set columns where the first SELECT of the UNION retrieved NOT NULL columns. The type and maximum length of the result column are now defined based on all parts of the UNION.

Columns of reduced subqueries were not always handled correctly. (Bug#679)

Double the required amount of memory was freed by the server.

CREATE FULLTEXT INDEX was not supported.

MyISAM tables with FULLTEXT indexes created in MySQL 4.0 were unreadable by MySQL 4.1.

When no host name is specified in SET PASSWORD FOR user, it now defaults to % instead of the current host.

Attempting to create a table containing a spatial (GIS) column using a storage engine that does not support spatial types cause the server to crash.

UNION operations that involved temporary tables could cause the server to crash.

UNION with an empty select list and a nonexistent column being used in some of the individual SELECT statements could cause the server to crash.

The final character was omitted from the output of USER(). (Bug#447)

Names of outer columns of subqueries in INSERT/REPLACE statements were not resolved correctly. (Bug#446)

Subqueries in ORDER BY and GROUP BY clauses were not processed correctly. (Bug#442)

Under certain, rare circumstances table corruption was caused by a DELETE from a large table with a “new” (created by MySQL-4.1) full-text index.

DELETE with ORDER BY and LIMIT could cause the server to crash.

The types and lengths of result set columns for UNION operations are now determined taking into account values for all SELECT statements in the UNION, and not just the first SELECT.

mysql parser erroneously interpreted a ; character within a multi-line comment (/* ... */) as a statement terminator.

The USER() function occasionally failed due an error in the size of the string allocated to it.

A SELECT that required a temporary table (marked by Using temporary in EXPLAIN output) and was used as a derived table in EXPLAIN command caused the server to crash. (Bug#251)

Using EXPLAIN on a derived table with a join caused the server to crash.

REPAIR TABLE ... USE_FRM could cause data loss when used with tables that contained TIMESTAMP columns and were created in 4.0.x.

Error-handling functions were not called properly when an error resulted from [CREATE | REPLACE| INSERT] ... SELECT statements.

LAST_INSERT_ID() now returns 0 if the last INSERT statement didn't insert any rows.