PRIMARY KEY in SQL.txt

// PRIMARY Key
-> The PRIMARY KEY constraint uniquely identifies each record in a database table.
Primaray keys must contains UNIQUE values. A primary key column cannot contain NULL values.
Most tables should have a primary key, and each table can have only ONE primary key.
syntax: CREATE TABLE example(s_id int (10) NOT NULL PRIMARY KEY ,name varchar
(50), roll_no int (10) ,number int (10));
 
 ex: desc example;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| s_id    | int         | NO   | PRI | NULL    |       |
| name    | varchar(50) | YES  |     | NULL    |       |
| roll_no | int         | YES  |     | NULL    |       |
| number  | int         | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+