MySQL update or insert for tables without primary key - mysql

Question

I know the simple way to perform update or insert is using 'REPLACE' but it needs a primary key, how about in the case of a table without primary key?
I have 5 columns in my table:
remark_id(the auto-increment primary key)
user_id
remark_user_id
remark
last_modified
I wish to check whether the pair of user_id and remark_user_id exists first before updating the remark, else a new row will be created to save the remark with the user_id and remark_user_id.
Here's my code
INSERT INTO `users_remark` (`user_id`, `remark_user_id`, `remark`)
SELECT 1,3 ,'testing123'
FROM dual
WHERE NOT EXISTS
(SELECT *
FROM `users_remark`
WHERE `user_id` = 1
AND `remark_user_id` = 3)
After running the SQL, nothing happens in my Database. No record was added or updated.
[Edited]
Code changes using IF...ELSE... but it comes with some syntax errors on first line
#1064 - 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 'IF EXISTS (SELECT * FROM users_remark WHERE user_id' at line 1
IF EXISTS (
SELECT * FROM `users_remark`
WHERE `user_id`=1 AND `remark_user_id` = 3
)
THEN UPDATE `users_remark` SET `remark` = 'testing123'
WHERE `user_id`=1 AND `remark_user_id` = 3
ELSE
INSERT INTO `users_remark` SET `remark` = 'testing123', `user_id`=1, `remark_user_id` = 3

Answer 1

Here is the query with both INSERT and UPDATE clauses (T-SQL syntax):
IF [condition here] BEGIN
UPDATE `users_remark`
SET `remark` = 'testing123'
WHERE `user_id`=1
AND `remark_user_id` = 3
END
ELSE BEGIN
INSERT INTO `users_remark` (`user_id`, `remark_user_id`, `remark`)
VALUES (1, 3, 'testing123)
END
EDIT: Same query with MySQL syntax
DECLARE #numrecords INT
SELECT #numrecords = count(*)
FROM `users_remark`
WHERE `user_id` = 1
AND `remark_user_id` = 3
IF #numrecords > 0 THEN
UPDATE `users_remark`
SET `remark` = 'testing123'
WHERE `user_id`=1
AND `remark_user_id` = 3
ELSE
INSERT INTO `users_remark` (`user_id`, `remark_user_id`, `remark`)
VALUES (1, 3, 'testing123)
END IF
Hope this will help you.

Answer 2

I finally try on putting code to php, it works and much easier to understand.
$checkRemark = mysqli_query($GLOBALS['db_conn'], "SELECT * FROM `users_remark` WHERE `user_id`=".$data['uid']." AND `remark_user_id` = ".$data['ruid']);
if (mysqli_num_rows($checkRemark)>0){
$remarkSql = "UPDATE `users_remark`
SET `remark` = '".$data['remark']."'
WHERE `user_id`=".$data['uid']."
AND `remark_user_id` = ".$data['ruid'];
} else {
$remarkSql = "INSERT INTO `users_remark` (`user_id`, `remark_user_id`, `remark`)
VALUES (".$data['uid'].", ".$data['ruid'].", '".$data['remark']."')";
}