The PARTITIONS table is a nonstandard table. It was added in MySQL 5.1.6.

Each record in this table corresponds to an individual partition or subpartition of a partitioned table.

TABLE_CATALOG: This column is always NULL.

TABLE_SCHEMA: This column contains the name of the database to which the table belongs.

TABLE_NAME: This column contains the name of the table containing the partition.

PARTITION_NAME: The name of the partition.

SUBPARTITION_NAME: If the PARTITIONS table record represents a subpartition, then this column contains the name of subpartition; otherwise it is NULL.

PARTITION_ORDINAL_POSITION: All partitions are indexed in the same order as they are defined, with 1 being the number assigned to the first partition. The indexing can change as partitions are added, dropped, and reorganized; the number shown is this column reflects the current order, taking into account any indexing changes.

SUBPARTITION_ORDINAL_POSITION: Subpartitions within a given partition are also indexed and reindexed in the same manner as partitions are indexed within a table.

PARTITION_METHOD: One of the values RANGE, LIST, HASH, LINEAR HASH, KEY, or LINEAR KEY; that is, one of the available partitioning types as discussed in Section 17.2, “Partition Types”.

SUBPARTITION_METHOD: One of the values HASH, LINEAR HASH, KEY, or LINEAR KEY; that is, one of the available subpartitioning types as discussed in Section 17.2.5, “Subpartitioning”.

PARTITION_EXPRESSION: This is the expression for the partitioning function used in the CREATE TABLE or ALTER TABLE statement that created the table's current partitioning scheme.

For example, consider a partitioned table created in the test database using this statement:

CREATE TABLE tp (
    c1 INT,
    c2 INT,
    c3 VARCHAR(25)
)
PARTITION BY HASH(c1 + c2)
PARTITIONS 4;

The PARTITION_EXPRESSION column in a PARTITIONS table record for a partition from this table displays c1 + c2, as shown here:

mysql> SELECT DISTINCT PARTITION_EXPRESSION
     >     FROM INFORMATION_SCHEMA.PARTITIONS
     >     WHERE TABLE_NAME='tp' AND TABLE_SCHEMA='test';
+----------------------+
| PARTITION_EXPRESSION |
+----------------------+
| c1 + c2              |
+----------------------+
1 row in set (0.09 sec)

SUBPARTITION_EXPRESSION: This works in the same fashion for the subpartitioning expression that defines the subpartitioning for a table as PARTITION_EXPRESSION does for the partitioning expression used to define a table's partitioning.

If the table has no subpartitions, then this column is NULL.

PARTITION_DESCRIPTION: This column is used for RANGE and LIST partitions. For a RANGE partition, it contains the value set in the partition's VALUES LESS THAN clause, which can be either an integer or MAXVALUE. For a LIST partition, this column contains the values defined in the partition's VALUES IN clause, which is a comma-separated list of integer values.

For partitions whose PARTITION_METHOD is other than RANGE or LIST, this column is always NULL.

TABLE_ROWS: The number of table rows in the partition.

For partitioned InnoDB tables, the row count given in the TABLE_ROWS column is only an estimated value used in SQL optimization, and may not always be exact.

AVG_ROW_LENGTH: The average length of the rows stored in this partition or subpartition, in bytes.

This is the same as DATA_LENGTH divided by TABLE_ROWS.

DATA_LENGTH: The total length of all rows stored in this partition or subpartition, in bytes — that is, the total number of bytes stored in the partition or subpartition.

MAX_DATA_LENGTH: The maximum number of bytes that can be stored in this partition or subpartition.

INDEX_LENGTH: The length of the index file for this partition or subpartition, in bytes.

DATA_FREE: The number of bytes allocated to the partition or subpartition but not used.

CREATE_TIME: The time of the partition's or subpartition's creation.

UPDATE_TIME: The time that the partition or subpartition was last modified.

CHECK_TIME: The last time that the table to which this partition or subpartition belongs was checked.

CHECKSUM: The checksum value, if any; otherwise, this column is NULL.

PARTITION_COMMENT: This column contains the text of any comment made for the partition.

The default value for this column is an empty string.

NODEGROUP: This is the nodegroup to which the partition belongs. This is relevant only to MySQL Cluster tables; otherwise the value of this column is always 0.

TABLESPACE_NAME: This column contains the name of tablespace to which the partition belongs. In MySQL 5.1, the value of this column is always DEFAULT.

A nonpartitioned table has one record in INFORMATION_SCHEMA.PARTITIONS; however, the values of the PARTITION_NAME, SUBPARTITION_NAME, PARTITION_ORDINAL_POSITION, SUBPARTITION_ORDINAL_POSITION, PARTITION_METHOD, SUBPARTITION_METHOD, PARTITION_EXPRESSION, SUBPARTITION_EXPRESSION, and PARTITION_DESCRIPTION columns are all NULL. (The PARTITION_COMMENT column in this case is blank.)

In MySQL 5.1, there is also only one record in the PARTITIONS table for a table using the NDBCLUSTER storage engine. The same columns are also NULL (or empty) as for a nonpartitioned table.