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MySQL 5.5 Reference Manual  /  INFORMATION_SCHEMA Tables  /  The INFORMATION_SCHEMA TABLES Table

21.22 The INFORMATION_SCHEMA TABLES Table

The TABLES table provides information about tables in databases.

The TABLES table has these columns:

  • TABLE_CATALOG

    The name of the catalog to which the table belongs. This value is always def.

  • TABLE_SCHEMA

    The name of the schema (database) to which the table belongs.

  • TABLE_NAME

    The name of the table.

  • TABLE_TYPE

    BASE TABLE for a table, VIEW for a view, or SYSTEM VIEW for an INFORMATION_SCHEMA table.

    The TABLES table does not list TEMPORARY tables.

  • ENGINE

    The storage engine for the table. See Chapter 14, The InnoDB Storage Engine, and Chapter 15, Alternative Storage Engines.

    For partitioned tables, ENGINE shows the name of the storage engine used by all partitions.

  • VERSION

    The version number of the table's .frm file.

  • ROW_FORMAT

    The row-storage format (Fixed, Dynamic, Compressed, Redundant, Compact). For MyISAM tables, Dynamic corresponds to what myisamchk -dvv reports as Packed. InnoDB table format is either Redundant or Compact when using the Antelope file format, or Compressed or Dynamic when using the Barracuda file format.

  • TABLE_ROWS

    The number of rows. Some storage engines, such as MyISAM, store the exact count. For other storage engines, such as InnoDB, this value is an approximation, and may vary from the actual value by as much as 40% to 50%. In such cases, use SELECT COUNT(*) to obtain an accurate count.

    TABLE_ROWS is NULL for INFORMATION_SCHEMA tables.

    For InnoDB tables, the row count is only a rough estimate used in SQL optimization. (This is also true if the InnoDB table is partitioned.)

  • AVG_ROW_LENGTH

    The average row length.

    Refer to the notes at the end of this section for related information.

  • DATA_LENGTH

    For MyISAM, DATA_LENGTH is the length of the data file, in bytes.

    For InnoDB, DATA_LENGTH is the approximate amount of memory allocated for the clustered index, in bytes. Specifically, it is the clustered index size, in pages, multiplied by the InnoDB page size.

    Refer to the notes at the end of this section for information regarding other storage engines.

  • MAX_DATA_LENGTH

    For MyISAM, MAX_DATA_LENGTH is maximum length of the data file. This is the total number of bytes of data that can be stored in the table, given the data pointer size used.

    Unused for InnoDB.

    Refer to the notes at the end of this section for information regarding other storage engines.

  • INDEX_LENGTH

    For MyISAM, INDEX_LENGTH is the length of the index file, in bytes.

    For InnoDB, INDEX_LENGTH is the approximate amount of memory allocated for non-clustered indexes, in bytes. Specifically, it is the sum of non-clustered index sizes, in pages, multiplied by the InnoDB page size.

    Refer to the notes at the end of this section for information regarding other storage engines.

  • DATA_FREE

    The number of allocated but unused bytes.

    InnoDB tables report the free space of the tablespace to which the table belongs. For a table located in the shared tablespace, this is the free space of the shared tablespace. If you are using multiple tablespaces and the table has its own tablespace, the free space is for only that table. Free space means the number of bytes in completely free extents minus a safety margin. Even if free space displays as 0, it may be possible to insert rows as long as new extents need not be allocated.

    For NDB Cluster, DATA_FREE shows the space allocated on disk for, but not used by, a Disk Data table or fragment on disk. (In-memory data resource usage is reported by the DATA_LENGTH column.)

    For partitioned tables, this value is only an estimate and may not be absolutely correct. A more accurate method of obtaining this information in such cases is to query the INFORMATION_SCHEMA PARTITIONS table, as shown in this example:

    SELECT SUM(DATA_FREE)
        FROM  INFORMATION_SCHEMA.PARTITIONS
        WHERE TABLE_SCHEMA = 'mydb'
        AND   TABLE_NAME   = 'mytable';

    For more information, see Section 21.13, “The INFORMATION_SCHEMA PARTITIONS Table”.

  • AUTO_INCREMENT

    The next AUTO_INCREMENT value.

  • CREATE_TIME

    When the table was created.

    Prior to MySQL 5.5.44, for partitioned InnoDB tables, the CREATE_TIME column shows NULL. This column shows the correct table creation time for such tables in MySQL 5.5.44 and later. (Bug #17299181, Bug #69990)

  • UPDATE_TIME

    When the data file was last updated. For some storage engines, this value is NULL. For example, InnoDB stores multiple tables in its system tablespace and the data file timestamp does not apply. Even with file-per-table mode with each InnoDB table in a separate .ibd file, change buffering can delay the write to the data file, so the file modification time is different from the time of the last insert, update, or delete. For MyISAM, the data file timestamp is used; however, on Windows the timestamp is not updated by updates, so the value is inaccurate.

    For partitioned InnoDB tables, UPDATE_TIME is always NULL.

  • CHECK_TIME

    When the table was last checked. Not all storage engines update this time, in which case, the value is always NULL.

    For partitioned InnoDB tables, CHECK_TIME is always NULL.

  • TABLE_COLLATION

    The table default collation. The output does not explicitly list the table default character set, but the collation name begins with the character set name.

  • CHECKSUM

    The live checksum value, if any.

  • CREATE_OPTIONS

    Extra options used with CREATE TABLE. The original options from when CREATE TABLE was executed are retained and the options reported here may differ from the active table settings and options.

    CREATE_OPTIONS shows partitioned if the table is partitioned.

  • TABLE_COMMENT

    The comment used when creating the table (or information as to why MySQL could not access the table information).

Notes

  • For NDB tables, the output of this statement shows appropriate values for the AVG_ROW_LENGTH and DATA_LENGTH columns, with the exception that BLOB columns are not taken into account.

  • For NDB tables, DATA_LENGTH includes data stored in main memory only; the MAX_DATA_LENGTH and DATA_FREE columns apply to Disk Data.

  • For NDB Cluster Disk Data tables, MAX_DATA_LENGTH shows the space allocated for the disk part of a Disk Data table or fragment. (In-memory data resource usage is reported by the DATA_LENGTH column.)

  • For MEMORY tables, the DATA_LENGTH, MAX_DATA_LENGTH, and INDEX_LENGTH values approximate the actual amount of allocated memory. The allocation algorithm reserves memory in large amounts to reduce the number of allocation operations.

  • For views, all TABLES columns are NULL except that TABLE_NAME indicates the view name and TABLE_COMMENT says VIEW.

Table information is also available from the SHOW TABLE STATUS and SHOW TABLES statements. See Section 13.7.5.37, “SHOW TABLE STATUS Syntax”, and Section 13.7.5.38, “SHOW TABLES Syntax”. The following statements are equivalent:

SELECT
    TABLE_NAME, ENGINE, VERSION, ROW_FORMAT, TABLE_ROWS, AVG_ROW_LENGTH,
    DATA_LENGTH, MAX_DATA_LENGTH, INDEX_LENGTH, DATA_FREE, AUTO_INCREMENT,
    CREATE_TIME, UPDATE_TIME, CHECK_TIME, TABLE_COLLATION, CHECKSUM,
    CREATE_OPTIONS, TABLE_COMMENT
  FROM INFORMATION_SCHEMA.TABLES
  WHERE table_schema = 'db_name'
  [AND table_name LIKE 'wild']

SHOW TABLE STATUS
  FROM db_name
  [LIKE 'wild']

The following statements are equivalent:

SELECT
  TABLE_NAME, TABLE_TYPE
  FROM INFORMATION_SCHEMA.TABLES
  WHERE table_schema = 'db_name'
  [AND table_name LIKE 'wild']

SHOW FULL TABLES
  FROM db_name
  [LIKE 'wild']

User Comments
User comments in this section are, as the name implies, provided by MySQL users. The MySQL documentation team is not responsible for, nor do they endorse, any of the information provided here.
  Posted by Naref Szolik on May 27, 2012
UPDATE_TIME only stores values for a subset of the available table storage engines.
  Posted by Chris Calender on March 7, 2013
UPDATE_TIME works for MyISAM, not InnoDB.

From my tests, it updated the timestamp on both DML and DDL operations.
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