Mysql: Swap data for different rows

问题:

Suppose a table fruits that looks like this:

------------------------------------------ | id |    name    |   color   | calories | ------------------------------------------ | 1  | apple      | red       | 20       | | 2  | orange     | orange    | 10       | | 3  | grapes     | green     | 5        | | 4  | bananas    | yellow    | 15       | | 5  | plum       | purple    | 25       | ------------------------------------------ 

How can I swap the values of a row, with another, leaving the id number intact?

Example:

SWAP ROW WITH ID "5" WITH ROW WITH ID "2" 

Result:

------------------------------------------ | id |    name    |   color   | calories | ------------------------------------------ | 1  | apple      | red       | 20       | | 2  | plum       | purple    | 25       | | 3  | grapes     | green     | 5        | | 4  | bananas    | yellow    | 15       | | 5  | orange     | orange    | 10       | ------------------------------------------ 

Note that all the values are intact except for the id. I need to do this with a really large list of values, so I need a one-liner, or at most, something that doesn't require the creation of temporary tables, and things like that.

Note: id is unique

Thank you

回答1:

You could use a join inequality to line up the rows you want to swap:

update fruit a  inner join fruit b on a.id  b.id    set a.color = b.color,        a.name = b.name,        a.calories = b.calories  where a.id in (2,5) and b.id in (2,5) 

http://sqlfiddle.com/#!2/18b9c/1

回答2:

Since ID is unique, it is difficult to just swap the IDs, it's easier to swap the column contents. A query like this might be what you need:

UPDATE   yourtable t1 INNER JOIN yourtable t2   ON (t1.id, t2.id) IN ((1,5),(5,1)) SET   t1.color = t2.color,   t1.name = t2.name,   t1.calories = t2.calories 

Please see fiddle here.

回答3:

Here's a way to store values temporarily without using a temp table or a dummy row in your fruit table:

SELECT name, color, calories FROM fruit WHERE id = 2 INTO @name, @color, @calories;  UPDATE fruit AS f1, fruit AS f2 SET  f1.name = f2.name, f2.name = @name,  f1.color = f2.color, f2.color = @color,  f1.calories = f2.calories, f2.calories = @calories WHERE (f1.id, f2.id) = (2, 5); 

Here's another solution that uses a dummy id value:

UPDATE fruit SET id = 0 WHERE id = 5; UPDATE fruit SET id = 5 WHERE id = 2; UPDATE fruit SET id = 2 WHERE id = 0; 

回答4:

If your operations are based on ID, and you want to swap entire rows, a fancy way of swapping UNIQUE IDs is to start numbering them at 1, and use 0 as a temporary value.

Another way of performing this is using an unsigned column, and using a designated value (ie.: -1) for temporary. I wouldn't really recommend the latter, as we are effectively wasting space with this method. See http://dev.mysql.com/doc/refman/5.0/en/numeric-type-overview.html for more details.

文章来源: Mysql: Swap data for different rows