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13.3.1 `DESCRIBE' Syntax (Get Information About Columns)
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{DESCRIBE | DESC} TBL_NAME [COL_NAME | WILD]
`DESCRIBE' provides information about a table's columns. It is a
shortcut for `SHOW COLUMNS FROM'. `SHOW COLUMNS' SHOW COLUMNS.
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 in
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)
The `Null' column indicates whether NULL values can be stored, with YES
displayed when NULL values are allowed.
The `Key' column indicates whether the field is indexed. A value of
`PRI' indicates that the field is part of the table's primary key.
`UNI' indicates that the field is part of a `UNIQUE' index. The `MUL'
value indicates that multiple occurrences of a given value allowed
within the field.
A field can be designated as `MUL' even if a `UNIQUE' index is used if
`NULL' values are allowed, as multiple rows in a `UNIQUE' index can hold
a `NULL' value if the column is not declared `NOT NULL'. Another cause
for `MUL' on a `UNIQUE' index is when two columns form a composite
`UNIQUE' index; while the combination of the columns will be unique,
each column can still hold multiple occurences of a given value. Note
that in a composite index only the leftmost field of the index will
have an entry in the `Key' column.
The `Default' column indicates the default value that is assigned to
the field.
The `Extra' column contains any additional information that is
available about a given field. In our example the `Extra' column
indicates that our `Id' column was created with the `AUTO_INCREMENT'
keyword.
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. Silent column changes.
The `DESCRIBE' statement is provided for Oracle compatibility.
The `SHOW CREATE TABLE' and `SHOW TABLE STATUS' statements also provide
information about tables. `SHOW' SHOW.
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