DESCRIBE Table

After a table has been created, you will often need to check exactly how it was defined — which columns it has, their data types, and which constraints apply to them. SQL provides the DESCRIBE statement to view the structure of an already created table:

DESCRIBE tablename;

MySQL also supports the short form DESC of DESCRIBE to get the description of a table — both do the same job. To retrieve details about the structure of the relation STUDENT, write DESC or DESCRIBE followed by the table name:

mysql> DESC STUDENT;
+--------------+-------------+------+-----+---------+-------+
| Field        | Type        | Null | Key | Default | Extra |
+--------------+-------------+------+-----+---------+-------+
| RollNumber   | int         | NO   | PRI | NULL    |       |
| SName        | varchar(20) | YES  |     | NULL    |       |
| SDateofBirth | date        | YES  |     | NULL    |       |
| GUID         | char(12)    | YES  |     | NULL    |       |
+--------------+-------------+------+-----+---------+-------+
4 rows in set (0.06 sec)

The output rewards a careful reading:

• Field lists the column names, in the order they were declared.
• Type shows the data type of each column — int, varchar(20), date, char(12) — exactly as chosen when the table was created.
• Null tells whether the column may hold NULL. RollNumber shows NO because it is the primary key; every other column shows YES, confirming that by default an attribute can take NULL values.
• Key marks the key columns: PRI against RollNumber identifies it as the primary key.
• Default shows the value a column takes when none is supplied — NULL for all columns here.

Now that STUDENT exists, the SHOW TABLES command no longer reports an empty set; it returns the table:

mysql> SHOW TABLES;
+------------------------------+
| Tables_in_studentattendance  |
+------------------------------+
| student                      | …