[SQL First Step] 5. Refer to Table Structure

DESC Command

TO see the structure of a table, use DESC. Returning table is an information of each column.

mysql> DESC sample21;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| no       | int         | YES  |     | NULL    |       |
| name     | varchar(20) | YES  |     | NULL    |       |
| birthday | date        | YES  |     | NULL    |       |
| address  | varchar(40) | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+
4 rows in set (0.01 sec)

DESC is not a SQL command.

• Field: Name of columns.
• Type: Datatype of columns.
• Null: Allow null value or not.
• Key: Key column or not.
• Default: Default value if omitted.

Datatype of SQL

There are multiple types of datatype in SQL.

• INTEGER: One integer. Decimal points are not allowed. int(10) means maximum length of integer is 10.
• CHAR: One character(string). CHAR(10) means maximum length of character is 10. If the length is shorter than 10, remaining parts will be filled with space.
• VARCHAR: Everything is same as CHAR, except the filling with space. Therefore the storage is variable according to the data.
• DATE: Store date(year-month-day)
• TIME: Store time(hour:minute:second).

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