Question

Is it possible to do a SELECT statement with a predetermined order, ie. selecting IDs 7,2,5,9 and 8 and returning them in that order, based on nothing more than the ID field?

Both these statements return them in the same order:

SELECT id FROM table WHERE id in (7,2,5,9,8)  

SELECT id FROM table WHERE id in (8,2,5,9,7) 

Answer 1

I didn’t think this was possible, but found a blog entry here that seems to do the type of thing you’re after:

SELECT id FROM table WHERE id in (7,2,5,9,8)  ORDER BY FIND_IN_SET(id,'7,2,5,9,8'); 

will give different results to

SELECT id FROM table WHERE id in (7,2,5,9,8)  ORDER BY FIND_IN_SET(id,'8,2,5,9,7'); 

FIND_IN_SET returns the position of id in the second argument given to it, so for the first case above, id of 7 is at position 1 in the set, 2 at 2 and so on – mysql internally works out something like

id | FIND_IN_SET ---|----------- 7  | 1 2  | 2 5  | 3 

then orders by the results of FIND_IN_SET.