Two ways to declare primary key when creating the table : Primary Key « Key « SQL / MySQL






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Two ways to declare primary key when creating the table

     
mysql>
mysql> CREATE TABLE IF NOT EXISTS cups
    -> (
    ->   id     INT     AUTO_INCREMENT PRIMARY KEY,
    ->   cup_pattern    VARCHAR(25)
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql>
mysql> # create a table called "saucers" with 2 columns
mysql> CREATE TABLE IF NOT EXISTS saucers
    -> (
    ->   id     INT     AUTO_INCREMENT,
    ->   scr_pattern    VARCHAR(25),
    ->   PRIMARY KEY(id)
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> # confirm the "cups" and "saucers" table format
mysql> EXPLAIN cups;
+-------------+-------------+------+-----+---------+----------------+
| Field       | Type        | Null | Key | Default | Extra          |
+-------------+-------------+------+-----+---------+----------------+
| id          | int(11)     | NO   | PRI | NULL    | auto_increment |
| cup_pattern | varchar(25) | YES  |     | NULL    |                |
+-------------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

mysql> EXPLAIN saucers;
+-------------+-------------+------+-----+---------+----------------+
| Field       | Type        | Null | Key | Default | Extra          |
+-------------+-------------+------+-----+---------+----------------+
| id          | int(11)     | NO   | PRI | NULL    | auto_increment |
| scr_pattern | varchar(25) | YES  |     | NULL    |                |
+-------------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

mysql>
mysql> # delete these sample tables
mysql> DROP TABLE cups, saucers;
Query OK, 0 rows affected (0.00 sec)








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