How to swap values of two rows in MySQL without violating unique constraint?

Question

I have a \"tasks\" table with a priority column, which has a unique constraint.

I\'m trying to swap the priority value of two rows, but I keep violating the constrai

Answer 1

you can achieve swapping your values with your above mentioned update statement, with a slight change in your key indexes.

CREATE TABLE `tasks` (   `id` int(11) NOT NULL,   `name` varchar(200) DEFAULT NULL,   `priority` varchar(45) DEFAULT NULL,   PRIMARY KEY (`id`,`priority`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

This will have a primary key index as a combination of id and priority. you cna then swap values.

UPDATE tasks 
SET priority = 
CASE
    WHEN priority=2 THEN 3 
    WHEN priority=3 THEN 2 
END 

WHERE priority IN (2,3);

I dont see any need of user variables or temp variables here. Hope this solves your issue :)