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17.2. Partition Types

This section discusses the types of partitioning which are available in MySQL 5.1. These include:

  • RANGE partitioning: Assigns rows to partitions based on column values falling within a given range. See Section 17.2.1, “RANGE Partitioning”.

  • LIST partitioning: Similar to partitioning by range, except that the partition is selected based on columns matching one of a set of discrete values. See Section 17.2.2, “LIST Partitioning”.

  • HASH partitioning: A partition is selected based on the value returned by a user-defined expression that operates on column values in rows to be inserted into the table. The function may consist of any expression valid in MySQL that yields a non-negative integer value. See Section 17.2.3, “HASH Partitioning”.

  • KEY partitioning: Similar to partitioning by hash, except that only one or more columns to be evaluated are supplied, and the MySQL server provides its own hashing function. The column or columns must contain only integer values. See Section 17.2.4, “KEY Partitioning”.

It is important to remember — regardless of the type of partitioning that you use — that partitions are always numbered automatically and in sequence when created, starting with 0. When a new row is inserted into a partitioned table, it is these partition numbers that are used in identifying the correct partition. For example, if your table uses 4 partitions, these partitions are numbered 0, 1, 2, and 3. For the RANGE and LIST partitioning types, it is necessary to ensure that there is a partition defined for each partition number. For HASH partitioning, the user function employed must return an integer value greater than 0. For KEY partitioning, this issue is taken care of automatically by the hashing function which the MySQL server employs internally.

Names of partitions generally follow the rules governing other MySQL identifiers, such as those for tables and databases. However, you should note that partition names are not case-sensitive. For example, the following CREATE TABLE statement fails as shown:

mysql> CREATE TABLE t2 (val INT)
    -> PARTITION BY LIST(val)(
    ->     PARTITION mypart VALUES IN (1,3,5),
    ->     PARTITION MyPart VALUES IN (2,4,6)
    -> );
ERROR 1488 (HY000): All partitions must have unique names in the table

Failure occurs because MySQL sees no difference between the partition names mypart and MyPart.

In the sections that follow, we do not necessarily provide all possible forms for the syntax that can be used for creating each partition type; this information may be found in Section 13.1.5, “CREATE TABLE Syntax”.


 
 
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