MySql Tutorial 5 - Getting Information About Databases and Tables

What if you forget the name of a database or table, or what the structure of a given table is (for example, what its columns are called)? MySQL addresses this problem through several statements that provide information about the databases and tables it supports.

You have previously seen SHOW DATABASES, which lists the databases managed by the server. To find out which database is currently selected, use the DATABASE() function:

mysql> SELECT DATABASE();
+------------+
| DATABASE() |
+------------+
| menagerie  |
+------------+

If you have not yet selected any database, the result is NULL.

To find out what tables the default database contains (for example, when you are not sure about the name of a table), use this command:

mysql> SHOW TABLES;

+---------------------+
| Tables_in_menagerie |
+---------------------+
| event               |
| pet                 |
+---------------------+

The name of the column in the output produced by this statement is
always
Tables_in_db_name,
where db_name is the name of the
database. See Section 12.5.4.25, “SHOW TABLES Syntax”, for more information.

If you want to find out about the structure of a table, the
DESCRIBE command is useful; it displays
information about each of a table's columns:

mysql> DESCRIBE pet;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name    | varchar(20) | YES  |     | NULL    |       |
| owner   | varchar(20) | YES  |     | NULL    |       |
| species | varchar(20) | YES  |     | NULL    |       |
| sex     | char(1)     | YES  |     | NULL    |       |
| birth   | date        | YES  |     | NULL    |       |
| death   | date        | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+

Field indicates the column name,
Type is the data type for the column,
NULL indicates whether the column can contain
NULL values, Key indicates
whether the column is indexed, and Default

specifies the column's default value. Extra
displays special information about columns; for example, if a
column was created with the AUTO_INCREMENT
option, this is shown here.