show table status

SHOW TABLE STATUS works likes SHOW TABLES, but provides a lot of information about each non-TEMPORARYtable. You can also get this list using the mysqlshow --status db_name command. The LIKE clause, if present, indicates which table names to match. The WHERE clause can be given to select rows using more general conditions, as discussed in Section 21.31, “Extensions to SHOW Statements”.

This statement also displays information about views.

SHOW TABLE STATUS output has the following columns:

• Name

  The name of the table.

• Engine

  The storage engine for the table. See Chapter 15, Alternative Storage Engines.

• Version

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

• Row_format

  The row-storage format (Fixed, Dynamic, Compressed, Redundant, Compact). For MyISAM tables, (Dynamiccorresponds to what myisamchk -dvv reports as Packed. The format of InnoDB tables is reported as Redundantor Compact. For the Barracuda file format of the InnoDB Plugin, the format may be Compressed or Dynamic.

• 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.

  The Rows value is NULL for tables in the INFORMATION_SCHEMA database.

• Avg_row_length

  The average row length.

• Data_length

  The length of the data file.

• Max_data_length

  The 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.

• Index_length

  The length of the index file.

• Data_free

  The number of allocated but unused bytes.

  This information is also shown for InnoDB tables (previously, it was in the Comment value). 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 completely free 1MB 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 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 21.12, “The INFORMATION_SCHEMA PARTITIONS Table”.

• Auto_increment

  The next AUTO_INCREMENT value.

• Create_time

  When the table was created.

• 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.

• Check_time

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

• Collation

  The table's character set and collation.

• Checksum

  The live checksum value (if any).

• Create_options

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

• Comment

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

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 NDBCLUSTER tables, the output of this statement shows appropriate values for the Avg_row_length andData_length columns, with the exception that BLOB columns are not taken into account

For views, all the fields displayed by SHOW TABLE STATUS are NULL except that Name indicates the view name andComment says view.

转载于:https://www.cnblogs.com/xiaotengyi/p/4158917.html