syntax error in ON UPDATE DUPLICATE KEY? - mysql

Question

I was trying to use the ON UPDATE DUPLICATE KEY clause for the first time, following this link
SQL - IF EXISTS UPDATE ELSE INSERT INTO
and I'm getting an error in my sql syntax:
SQLSTATE[42000]: Syntax error or access violation: 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 ''AJAY KUMAR')'
at line 2 The SQL being executed was: INSERT INTO fee_acc_balance
(guardian_name, account_no, paid_amount, due, days_overdue,
total_fees, updated_on) VALUES ('AJAY KUMAR', '10', 0, 12550, 0,
12550, '2017-02-10 21:28:05') ON DUPLICATE KEY UPDATE guardian_name =
VALUES ('AJAY KUMAR') Error Info: Array ( [0] => 42000 [1] => 1064 [2]
=> You have an error..
The unique key in my case is account_no, and this is my sql :
INSERT INTO fee_acc_balance (guardian_name, account_no, paid_amount, due, days_overdue, total_fees, updated_on)
VALUES ('$father_name', '$account->account_no', $payments, $sum, 0, $sum,'$now')
ON DUPLICATE KEY UPDATE guardian_name = VALUES ('$father_name')
Where does the error lie?

Answer 1

You cannot specify an absolute value in ON DUPLICATE KEY UPDATE:
ON DUPLICATE KEY UPDATE guardian_name = VALUES ('$father_name')
Try with
ON DUPLICATE KEY UPDATE guardian_name = VALUES(guardian_name)
Notice that the right part of the assignment is the new field coming in from VALUES, and the left side is the extant record; "UPDATE a = VALUES(a)" means "put the a from VALUES into the record", not "leave everything as it is".
Also, you may want to write variables in curly brackets:
...VALUES ('{$father_name}', '{$account->account_no}', {$payments}, {$sum}, 0, {$sum}, '{$now}')
or even better use PREPAREd statement with PDO:
$stmt->prepare("INSERT... VALUES(?, ?, ?, ?, 0, ?, ?)");
$stmt->execute([
$father_name,
$account->account_no,
$payments,
$sum,
$sum,
$now
]);
and, better still, bound parameters.
Otherwise, strange things might happen if the guardian name is Ajay Al'Kumar (note the quote mark) or a string value is passed instead of an integer one.