Spec-Zone .ru
спецификации, руководства, описания, API
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Spec-Zone .ru
спецификации, руководства, описания, API
|
SHOW TABLE STATUS [{FROM | IN} db_name] [LIKE 'pattern' | WHERE expr]
SHOW TABLE STATUS works likes SHOW TABLES, but provides a lot of information about each non-TEMPORARY table. 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
20.32, "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 14, 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, (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 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 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 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 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 views, all the fields displayed by SHOW
TABLE STATUS are NULL except that Name
indicates the view name and Comment says view.