MySQL禁止具有2个相同列值的行与另一行

Question

This is my MySQL table:

• The left column auto increments.
• The center column is the id# of the user.
• The right column is the id# of a post that they like.

I am inserting data into the table like so:

$stmt = $db->prepare("INSERT INTO likes (user_id,post_id) VALUES (?,?)");
$stmt->execute(array($_SESSION['user'],$_POST['id']));

This works fine, but as you can see the MySQL table has two identical rows (id's 3 & 4) which both have a user_id of 5 and a post_id of 196. In other words my MySQL table records that the user with id = 5 likes the post with id = 196 two times. how do I disallow a situation where there are two rows that have identical user_id's and identical post_id's

Answer 1

You need to set a unique constraint on the user_id and post_id columns