Question

I have a simple query that increases the value of a field by 1.
Now I used to loop over all id’s and fire a query for each of them, but now that things are getting a bit resource heavy I wanted to optimize this. Normally I would just do

UPDATE table SET field = field + 1 WHERE id IN (all the ids here)

but now I have the problem that there are id’s that occur twice (or more, I can’t know that on forehand).
Is there a way to have the query run twice for id 4 if the query looks like this:

UPDATE table SET field = field + 1 WHERE id IN (1, 2, 3, 4, 4, 5)

Thanks,

lordstyx

Edit: sorry for not being clear enough.
The id here is an auto inc field, so it are all unique ID’s. the id’s that have to be updated are indirectly comming from users, so I can’t predict which id is going to occur how often.
If there are the ID’s (1, 2, 3, 4, 4, 5) I need the field of row with id 4 to be incremented with 2, and all the rest with 1.

Answer 1

If (1, 2, 3, 4, 4, 5) comes from a SELECT id ... query, then you can do something like this:

UPDATE yourTable 
  JOIN 
    ( SELECT id
           , COUNT(id) AS counter 
      ....
      GROUP BY id
    ) AS data
    ON yourTable.id = data.id
SET yourTable.field = yourTable.field + data.counter 
;

Since the input comes from users, perhaps you can manipulate it a bit. Change (1, 2, 3, 4, 4, 5) to (1), (2), (3), (4), (4), (5).

Then (having created a temporary table):

CREATE TABLE tempUpdate
( id INT )
;

Do the following procedure:

1. add the values in the temporary table,
2. run the update and
3. delete the values.

Code:

INSERT INTO TempUpdate
VALUES (1), (2), (3), (4), (4), (5)
;

UPDATE yourTable 
  JOIN 
    ( SELECT id
           , COUNT(id) AS counter 
      FROM TempUpdate
      GROUP BY id
    ) AS data
    ON yourTable.id = data.id
SET yourTable.field = yourTable.field + data.counter 
;

DELETE FROM TempUpdate
;