13.7.5.5 SHOW COLUMNS Syntax

SHOW [FULL] COLUMNS {FROM | IN} tbl_name [{FROM | IN} db_name]
    [LIKE 'pattern' | WHERE expr]

SHOW COLUMNS displays information about the columns in a given table. It also works for views as of MySQL 5.0.1. The LIKE clause, if present, indicates which column names to match. The WHERE clause can be given to select rows using more general conditions, as discussed in Section 19.18, “Extensions to SHOW Statements”.

mysql> SHOW COLUMNS FROM City;
+------------+----------+------+-----+---------+----------------+
| Field      | Type     | Null | Key | Default | Extra          |
+------------+----------+------+-----+---------+----------------+
| Id         | int(11)  | NO   | PRI | NULL    | auto_increment |
| Name       | char(35) | NO   |     |         |                |
| Country    | char(3)  | NO   | UNI |         |                |
| District   | char(20) | YES  | MUL |         |                |
| Population | int(11)  | NO   |     | 0       |                |
+------------+----------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

If the data types differ from what you expect them to be based on a CREATE TABLE statement, note that MySQL sometimes changes data types when you create or alter a table. The conditions under which this occurs are described in Section 13.1.10.3, “Silent Column Specification Changes”.

The FULL keyword causes the output to include the column collation and comments, as well as the privileges you have for each column.

You can use db_name.tbl_name as an alternative to the tbl_name FROM db_name syntax. In other words, these two statements are equivalent:

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

SHOW COLUMNS displays the following values for each table column:

Field indicates the column name.

Type indicates the column data type.

Collation indicates the collation for nonbinary string columns, or NULL for other columns. This value is displayed only if you use the FULL keyword.

The Null field contains YES if NULL values can be stored in the column. If not, the column contains NO as of MySQL 5.0.3, and '' before that.

The Key field indicates whether the column is indexed:

If more than one of the Key values applies to a given column of a table, Key displays the one with the highest priority, in the order PRI, UNI, MUL.

A UNIQUE index may be displayed as PRI if it cannot contain NULL values and there is no PRIMARY KEY in the table. A UNIQUE index may display as MUL if several columns form a composite UNIQUE index; although the combination of the columns is unique, each column can still hold multiple occurrences of a given value.

Before MySQL 5.0.11, if the column permits NULL values, the Key value can be MUL even when a single-column UNIQUE index is used. The rationale was that multiple rows in a UNIQUE index can hold a NULL value if the column is not declared NOT NULL. As of MySQL 5.0.11, the display is UNI rather than MUL regardless of whether the column permits NULL; you can see from the Null field whether or not the column can contain NULL.

The Default field indicates the default value that is assigned to the column. This is NULL if the column has an explicit default of NULL. As of MySQL 5.0.50, Default is also NULL if the column definition has no DEFAULT clause.

The Extra field contains any additional information that is available about a given column. The value is auto_increment for columns that have the AUTO_INCREMENT attribute and empty otherwise.

Privileges indicates the privileges you have for the column. This value is displayed only if you use the FULL keyword.

Comment indicates any comment the column has. This value is displayed only if you use the FULL keyword.

SHOW FIELDS is a synonym for SHOW COLUMNS. You can also list a table's columns with the mysqlshow db_name tbl_name command.

The DESCRIBE statement provides information similar to SHOW COLUMNS. See Section 13.8.1, “DESCRIBE Syntax”.

The SHOW CREATE TABLE, SHOW TABLE STATUS, and SHOW INDEX statements also provide information about tables. See Section 13.7.5, “SHOW Syntax”.