在列中设置唯一值，如果不唯一，则将其他值向下移动

Question

I have problem with this. What I need is to get unique values in column called order in my event table. How this thing should behave: for example I have table `event

| id | name    | order |
|----|---------|-------|
| 1  | walking | 1     |
| 2  | diving  | 2     |
| 3  | skating | 3     |

for example when I try to update skating order to 1 I will get

| id | name    | order |
|----|---------|-------|
| 3  | skating | 1     |
| 1  | walking | 2     |
| 2  | diving  | 3     |

Have no idea how to do it, tried this but it doesn't work for me:

Yii::$app->db->createCommand("
        SET @rownum :=0;
        UPDATE  " . self::tableName() . "
        LEFT JOIN (
            SELECT id,  (@rownum := @rownum + 1) AS rowNumber
            FROM " . self::tableName() . "
            ORDER BY order ASC
        ) as tmp_table
        on tmp_table.id = " . self::tableName() . ".id
        SET " . self::tableName() . ".order = tmp_table.rowNumber"
    )->execute();

If it's not understandable for you, ask me I will try to explain all the things.

Answer 1

You don't need to regenerate all the orders using a user variable, since you're just adding 1 to them, except for the element that moves into position 1 . So you can do it with IF or CASE .

UPDATE yourTable
SET `order` = CASE name
    WHEN 'skating' THEN 1
    ELSE `order` + 1
END

If you need to be able to move the element to some place other than 1 , then it gets a little more complicated:

UPDATE yourTable
SET `order` = CASE
    WHEN name = 'skating' THEN @newpos
    WHEN `order` >= @newpos THEN `order` + 1
END