Question

I’m attempting to construct an SQL statement for MySQL that will update a single row in a group. Taking the records below I need to update the IsPrimary flag so that the earliest record for each user is set to 1.

 ID       | UserID      | Inserted    | IsPrimary
----------|-------------|-------------|----------
000f83    | 79b8c3      | 2012-03-14  | 0
001401    | 79b8c3      | 2012-03-15  | 0
002e7d    | 4652a2      | 2012-02-22  | 0
003ca6    | 4652a2      | 2012-02-13  | 0  

So the above records would end up as:

 ID       | UserID      | Inserted    | IsPrimary
----------|-------------|-------------|----------
000f83    | 79b8c3      | 2012-03-14  | 1
001401    | 79b8c3      | 2012-03-15  | 0
002e7d    | 4652a2      | 2012-02-22  | 0
003ca6    | 4652a2      | 2012-02-13  | 1  

Answer 1

Give this a ry:

update t, (
  select t1.id anId from t t1
  left join t t2
  on t1.userId = t2.userId and t1.inserted > t2.inserted
  where t2.inserted is null
) s
set IsPrimary = 1
where t.id = anId

Here is the fiddle.