Question

I have a need to do an insert to MySQL where a record does not exist in the destination table already

my query

INSERT INTO comment (`mid`, `pid`, `comment_text`, `comment_date`, `comment_type`) 
 VALUES (180, 2, NULL, '2012-07-26 10:19:00', 'tag')  WHERE NOT EXISTS ( SELECT * FROM `comment` WHERE `mid`=180 AND `pid`=2 AND `comment_type`='tag')

however when this runs I get this error

You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use
near ‘WHERE NOT EXISTS ( SELECT * FROM comment WHERE mid=180 AND
`pid’ at line 2

Any ideas essentially i want to stop duplicate rows being added to this table when they match the values

Answer 1

try:

INSERT IGNORE INTO comment
(
 `mid`, `pid`, `comment_text`, `comment_date`, `comment_type`
)
(
    SELECT 180, 2, NULL, '2012-07-26 10:19:00', 'tag'
    FROM comment
    WHERE `mid`=180 AND
          `pid`=2 AND
          `comment_type`='tag'
    LIMIT 1
);

EDIT: Better way to do this:

to remove duplicates from a table see here

ALTER IGNORE TABLE comment ADD UNIQUE KEY ix1(mid, pid, comment_type);

INSERT IGNORE INTO comment
(
 `mid`, `pid`, `comment_text`, `comment_date`, `comment_type`
)
VALUES 
(
 SELECT 180, 2, NULL, '2012-07-26 10:19:00', 'tag'
);