MySQL Reference Manual for version 4.0.18.

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13.5.3.1 Retrieving Information about Database, Tables, Columns, and Indexes

You can use db_name.tbl_name as an alternative to the tbl_name FROM db_name syntax. These two statements are equivalent:

 
mysql> SHOW INDEX FROM mytable FROM mydb;
mysql> SHOW INDEX FROM mydb.mytable;

SHOW DATABASES lists the databases on the MySQL server host. You can also get this list using the mysqlshow command line tool. In version 4.0.2 you will see only those databases for which you have some kind of privilege, if you don't have the global SHOW DATABASES privilege.

SHOW TABLES lists the tables in a given database. You can also get this list using the mysqlshow db_name command.

Note: If a user doesn't have any privileges for a table, the table will not show up in the output from SHOW TABLES or mysqlshow db_name.

SHOW OPEN TABLES lists the tables that are currently open in the table cache. See section 7.4.8 How MySQL Opens and Closes Tables. The Comment field tells how many times the table is cached and in_use.

SHOW COLUMNS lists the columns in a given table. If you specify the FULL option, you will also get the privileges you have for each column. If the column types are different from what you expect them to be based on a CREATE TABLE statement, note that MySQL sometimes changes column types. See section 13.2.5.1 Silent Column Specification Changes. As of MySQL 4.1, the FULL keyword also causes any per-column comments to be displayed.

The DESCRIBE statement provides information similar to SHOW COLUMNS. See section DESCRIBE.

SHOW FIELDS is a synonym for SHOW COLUMNS, and SHOW KEYS is a synonym for SHOW INDEX. You can also list a table's columns or indexes with mysqlshow db_name tbl_name or mysqlshow -k db_name tbl_name.

SHOW INDEX returns the index information in a format that closely resembles the SQLStatistics call in ODBC. The following columns are returned:

starting with 1. In MySQL, this can have values `A' (Ascending) or NULL (Not sorted). This is updated by running myisamchk -a. column is only partly indexed. NULL if the entire column is indexed. in MySQL < 4.0.2 whether or not index is FULLTEXT.
Column Meaning
Table Name of the table.
Non_unique 0 if the index can't contain duplicates, 1 if it can.
Key_name Name of the index.
Seq_in_index Column sequence number in index,
Column_name Column name.
Collation How the column is sorted in the index.
Cardinality Number of unique values in the index.
Sub_part Number of indexed characters if the
Packed Indicates how the key is packed. NULL if it is not.
Null Contains YES if the column may contain NULL.
Index_type Index method used.
Comment Various remarks. For now, it tells

Note that as the Cardinality is counted based on statistics stored as integers, it's not necessarily accurate for small tables.

The Packed and Comments columns were added in MySQL 3.23.0. The Null and Index_type columns were added in MySQL 4.0.2.


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