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 18.2, “Partitioning 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 18.2.5, “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.

Beginning with MySQL Cluster NDB 7.0.22 and MySQL Cluster NDB 7.1.11, TABLE_ROWS shows correct information for NDB tables. Previously, for partitions of NDB tables, the TABLE_ROWS column value was always 0.

For NDB tables, you can also obtain this information using the ndb_desc utility.

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.

Beginning with MySQL Cluster NDB 7.0.22 and MySQL Cluster NDB 7.1.11, AVG_ROW_LENGTH includes statistics for partitions of NDB tables, whether the tables use implicit or explicit partitioning. (Previously the value of this column was always 0 for partitions of NDB tables.)

You can also obtain equivalent information using the ndb_desc utility.

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.

Beginning with MySQL Cluster NDB 7.0.22 and MySQL Cluster NDB 7.1.11, DATA_LENGTH shows correct information for in-memory data in NDB tables. Previously, for partitions of NDB tables, the DATA_LENGTH column value was always 0.

For NDB tables, you can also obtain this information using the ndb_desc utility.

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

Beginning with MySQL Cluster NDB 7.0.22 and MySQL Cluster NDB 7.1.11, MAX_DATA_LENGTH shows the space allocated for the disk part of a MySQL Cluster Disk Data table or fragment. (Previously, for partitions of NDB tables, the MAX_DATA_LENGTH column value was always NULL.)

For NDB tables, you can also obtain this information using the ndb_desc utility.

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

For partitions of NDB tables, whether the tables use implicit or explicit partitioning, the INDEX_LENGTH column value is always 0. However, you can obtain equivalent information using the ndb_desc utility.

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

For MySQL Cluster Disk Data tables, beginning with MySQL Cluster NDB 7.0.22 and MySQL Cluster NDB 7.1.11, DATA_FREE shows the space allocated on disk for, but not used by, a Disk Data table or fragment on disk. (Previously, for partitions of NDB tables, the value of this column was always 0.)

For NDB tables, you can also obtain this information using the ndb_desc utility.

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.

In MySQL 5.1, the display width of this column is 80 characters, and partition comments which exceed this length are truncated to fit. This issue is fixed in MySQL 5.6. (Bug #11748924, Bug #37728)

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 the tablespace to which the partition belongs. Currently, 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.