show table status

• MySQL 5.6 

SHOW TABLE STATUS 用法

SHOW TABLE STATUS [{FROM | IN} db_name]
    [LIKE 'pattern' | WHERE expr]

SHOW TABLE STATUS 的工作機制像 SHOW TABLES, 但是對於非 TEMPORARY table提供了更多的信息. 你也可以使用下面的命令來得到想要的內容： mysqlshow --status db_name .LIKE 這個關鍵字可以匹配你要想指定那個表, if present, indicates which table names to match. The WHERE clause can be given to select rows using more general conditions, as discussed inSection 20.32, “Extensions to SHOW Statements”.

This statement also displays information about views.

SHOW TABLE STATUS 會有下面這些列:

• Name

  The name of the table.

  表名

• Engine

  The storage engine for the table. See Chapter 14, Storage Engines.

  表的存儲引擎

• Version

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

  .frm 文件的version版本號

• Row_format

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

  row-storage 格式有這樣.（Fixed, Dynamic, Compressed, Redundant,Compact)對於MyISAM這樣的表（Dynamic 對應着((what myisamchk -dvv reports as Packed.Innodb)) 的表是Redundant 或者 Compact。對於InnoDB Plugin Barracuda 文件的，一般爲Compressed 或者 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.

  行數。一些存儲引擎，例如MyISAM，會存儲額外的個數。對於其他的存儲引擎，例如InnoDB，這個值會是估算只，對於實際的數字會有40%-50%的範圍估算。在這樣的case中，通常使用SELECT COUNT(*)來增加準確度。

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

  在INFORMATION_SCHEMA 這樣的數據庫中，Rows 都爲 NULL  

• Avg_row_length

  行長度

• Data_length

  數據文件長度

• Max_data_length

  數據文件最大值. 這個是是用bytes來統計表中數據的

• Index_length

  索引長度

• Data_free

  The number of allocated but unused bytes.

  分配的數值，而不針對unused 

  This information is also shown for InnoDB tables (previously, it was in theComment 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 20.14, “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 alwaysNULL.

• 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 NDB 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 and Comment says view.