MySQL in a Nutshell, 2nd Edition

Name

DESCRIBE

Synopsis

{DESCRIBE|DESC} table [column]

This statement displays information about the columns of a given table. The DESCRIBE keyword can be abbreviated to DESC:

DESCRIBE workreq;

+--------------------+---------+------+-----+---------+----------------+
| Field              | Type    | Null | Key | Default | Extra          |
+--------------------+---------+------+-----+---------+----------------+
| req_id             | int(11) | NO   | PRI | NULL    | auto_increment | 
| client_id          | int(11) | YES  |     | NULL    |                | 
| client_description | text    | YES  | MUL | NULL    |                | 
| technician_notes   | text    | YES  |     | NULL    |                | 
+--------------------+---------+------+-----+---------+----------------+

For information on a specific column, supply only the column name. For information on multiple columns but not all columns, you can supply a name pattern within quotes and use the wildcard characters % and _. Quotes around the string aren’t necessary unless the string contains spaces.

To list the columns in the workreq table that have names beginning with the characters client, enter the following:

DESCRIBE workreq 'client%';

+--------------------+---------+------+-----+---------+-------+
| Field              | Type    | Null | Key | Default | Extra |
+--------------------+---------+------+-----+---------+-------+
| client_id          | int(11) | YES  |     | NULL    |       | 
| client_description | text    | YES  | MUL | NULL    |       | 
+--------------------+---------+------+-----+---------+-------+

Notice that the keyword LIKE is not used. The fields in the results have the following meanings:

Field: Lists the name of each column in the table.
Type: Shows the data type of each column.
Null: Indicates whether the column in the table may contain a NULL value.
Default: Shows the default value of the column.
Key: Indicates what type of key the column is. If this field is empty, the column is not indexed. A value of PRI indicates a PRIMARY KEY column, UNI indicates a UNIQUE indexed column, and MUL means that multiple occurrences, or duplicate values, are permitted for the column. This is allowed because the column is only one of multiple columns making up an index.
Extra: Lists any extra information particular to the column.

To understand how the options you use when creating or altering a table affect the output of DESCRIBE, let’s look at the schema of the table shown in an earlier example:

SHOW CREATE TABLE workreq \G

*************************** 1. row ***************************
       Table: workreq
Create Table: CREATE TABLE 'workreq' (
  'req_id' int(11) NOT NULL AUTO_INCREMENT,
  'client_id' int(11) DEFAULT NULL,
  'client_description' text,
  'technician_notes' text,
  PRIMARY KEY ('req_id'),
  FULLTEXT KEY 'notes_index' ('client_description','technician_notes')
) ENGINE=MyISAM DEFAULT CHARSET=latin1

The results of this SHOW CREATE TABLE statement indicate that client_description is part of the index called notes_index. The other column that is part of that index is technician_notes. Notice in the results of the earlier DESCRIBE statement that only the first column of the index is marked MUL.

Table of Contents for MySQL in a Nutshell, 2nd Edition

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Table of Contents for
MySQL in a Nutshell, 2nd Edition