The following features are implemented in MySQL 5.0:

**Information Schema.**The introduction of the`INFORMATION_SCHEMA`

database in MySQL 5.0 provided a standards-compliant means for accessing the MySQL Server's metadata; that is, data about the databases (schemas) on the server and the objects which they contain. See Chapter 19,*INFORMATION_SCHEMA Tables*.**Instance Manager.**Can be used to start and stop the MySQL Server, even from a remote host. See Section 4.6.10, “**mysqlmanager**— The MySQL Instance Manager”.**Precision Math.**MySQL 5.0 introduced stricter criteria for acceptance or rejection of data, and implemented a new library for fixed-point arithmetic. These contributed to a much higher degree of accuracy for mathematical operations and greater control over invalid values. See Section 12.17, “Precision Math”.**Storage Engines.**New storage engines were added and performance of others was improved.New storage engines in MySQL 5.0 include

`ARCHIVE`

and`FEDERATED`

. See Section 14.8, “The ARCHIVE Storage Engine”, and Section 14.7, “The FEDERATED Storage Engine”.Performance Improvements in the

`InnoDB`

Storage Engine:New compact storage format which can save up to 20% of the disk space required in previous MySQL/

`InnoDB`

versions.Faster recovery from a failed or aborted

`ALTER TABLE`

.Faster implementation of

`TRUNCATE TABLE`

.

Performance Improvements in the

`NDBCLUSTER`

Storage Engine:Faster handling of queries that use

`IN`

and`BETWEEN`

.Condition pushdown: In cases involving the comparison of an unindexed column with a constant, this condition is “pushed down” to the cluster where it is evaluated in all partitions simultaneously, eliminating the need to send nonmatching records over the network. This can make such queries 10 to 100 times faster than in MySQL 4.1 Cluster.

See Section 13.8.2, “EXPLAIN Syntax”, for more information.

(See Chapter 17,

*MySQL Cluster*.)

**Stored Routines.**MySQL 5.0 added support for stored procedures and stored functions. See Section 18.2, “Using Stored Routines (Procedures and Functions)”.**Triggers.**MySQL 5.0 added limited support for triggers. See Section 18.3, “Using Triggers”.**Views.**MySQL 5.0 added support for named, updatable views. See Section 18.4, “Using Views”.**Cursors.**Elementary support for server-side cursors. For information about using cursors within stored routines, see Section 13.6.6, “Cursors”. For information about using cursors from within the C API, see Section 20.6.11.3, “mysql_stmt_attr_set()”.**Strict Mode and Standard Error Handling.**MySQL 5.0 added a strict mode where by it follows standard SQL in a number of ways in which it did not previously. Support for standard SQLSTATE error messages was also implemented. See Section 5.1.7, “Server SQL Modes”.**VARCHAR Data Type.**The effective maximum length of a`VARCHAR`

column was increased to 65,535 bytes, and stripping of trailing whitespace was eliminated.`VARCHAR`

in MySQL 5.0 is more efficient than in previous versions, due to the elimination of the old (and nonstandard) removal of trailing spaces during retrieval. (The actual maximum length of a`VARCHAR`

is determined by the maximum row size and the character set you use. The maximum*effective*column length is subject to a row size of 65,535 bytes, which is shared among all columns.) See Section 11.4, “String Types”.**BIT Data Type.**A true`BIT`

column type is available that can be used to store numbers in binary notation. This type is much more efficient for storage and retrieval of Boolean values than the workarounds required in MySQL in versions previous to 5.0. See Section 11.1.1, “Numeric Type Overview”.**Optimizer enhancements.**Several optimizer improvements were made to improve the speed of certain types of queries and in the handling of certain types. These include:MySQL 5.0 introduces a new “greedy” optimizer which can greatly reduce the time required to arrive at a query execution plan. This is particularly noticeable where several tables are to be joined and no good join keys can otherwise be found. Without the greedy optimizer, the complexity of the search for an execution plan is calculated as

, where!`N`

is the number of tables to be joined. The greedy optimizer reduces this to`N`

, where!/(`N`

-1)!`D`

is the depth of the search. Although the greedy optimizer does not guarantee the best possible of all execution plans (this is currently being worked on), it can reduce the time spent arriving at an execution plan for a join involving a great many tables—30, 40, or more—by a factor of as much as 1,000. This should eliminate most if not all situations where users thought that the optimizer had hung when trying to perform joins across many tables.`D`

Use of the

*Index Merge*method to obtain better optimization of`AND`

and`OR`

relations over different keys. (Previously, these were optimized only where both relations in the`WHERE`

clause involved the same key.) This also applies to other one-to-one comparison operators (`>`

,`<`

, and so on), including`=`

and the`IN`

operator. This means that MySQL can use multiple indexes in retrieving results for conditions such as`WHERE key1 > 4 OR key2 < 7`

and even combinations of conditions such as`WHERE (key1 > 4 OR key2 < 7) AND (key3 >= 10 OR key4 = 1)`

. See Section 8.2.1.4, “Index Merge Optimization”.A new equality detector finds and optimizes “hidden” equalities in joins. For example, a

`WHERE`

clause such ast1.c1=t2.c2 AND t2.c2=t3.c3 AND t1.c1 < 5

implies these other conditions

t1.c1=t3.c3 AND t2.c2 < 5 AND t3.c3 < 5

These optimizations can be applied with any combination of

`AND`

and`OR`

operators. See Section 8.2.1.9, “Nested Join Optimization”, and Section 8.2.1.10, “Outer Join Simplification”.Optimization of

`NOT IN`

and`NOT BETWEEN`

relations, reducing or eliminating table scans for queries making use of them by mean of range analysis. The performance of MySQL with regard to these relations now matches its performance with regard to`IN`

and`BETWEEN`

.

**XA Transactions.**MySQL 5.0 supports XA (distributed) transactions. See Section 13.3.7, “XA Transactions”.