{DESCRIBE | DESC} tbl_name [col_name | wild]

DESCRIBE provides information about the columns in a table. It is a shortcut for SHOW COLUMNS FROM. (See Section 13.5.4.3, “SHOW COLUMNS Syntax”.)

col_name can be a column name, or a string containing the SQL ‘%’ and ‘_’ wildcard characters to obtain output only for the columns with names matching the string. There is no need to enclose the string within quotes unless it contains spaces or other special characters.

mysql> DESCRIBE city;
+------------+----------+------+-----+---------+----------------+
| Field      | Type     | Null | Key | Default | Extra          |
+------------+----------+------+-----+---------+----------------+
| Id         | int(11)  |      | PRI | NULL    | auto_increment |
| Name       | char(35) |      |     |         |                |
| Country    | char(3)  |      | UNI |         |                |
| District   | char(20) | YES  | MUL |         |                |
| Population | int(11)  |      |     | 0       |                |
+------------+----------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

Field indicates the column name.

The Null field indicates whether NULL values can be stored in the column, with YES displayed when NULL values are allowed.

The Key field indicates whether the column is indexed. A value of PRI indicates that the column is part of the table's primary key. UNI indicates that the column is part of a UNIQUE index. The MUL value indicates that multiple occurrences of a given value are allowed within the column.

One reason for MUL to be displayed on a UNIQUE index is that 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. Note that in a composite index, only the leftmost column of the index has an entry in the Key field.

If the column allows NULL values, the Key value can be MUL even when a UNIQUE index is used. The rationale is that multiple rows in a UNIQUE index can hold a NULL value if the column is not declared NOT NULL. (This behavior changes in MySQL 5.0.)

The Default field indicates the default value that is assigned to the column.

The Extra field contains any additional information that is available about a given column. In the example shown, the Extra field indicates that the Id column was created with the AUTO_INCREMENT keyword.

If the data types are different from what you expect them to be based on a CREATE TABLE statement, note that MySQL sometimes changes data types. See Section 13.1.5.1, “Silent Column Specification Changes”.

The DESCRIBE statement is provided for compatibility with Oracle.

The SHOW CREATE TABLE and SHOW TABLE STATUS statements also provide information about tables. See Section 13.5.4, “SHOW Syntax”.