Question

I have a table like:

id(int)    flag(int)    price(float)

1          0            50
2                       400
3          4            200
4          3            150
5          3            100
6          3            400
7          2            120

I’d like to select all rows that have distinct flag, choosing the lowest price on every group of flag
So, in this example I’d get:

id(int)    flag(int)    price(float)

1          0            50
2                       400
3          4            200
5          3            100
7          2            120

Note that flag is not mandatory, so it can have a value (int) or nothing (null).

Regards

EDIT:

Just to make it mre clear.

I want to select all the rows that have an id and a price, all of them, without filtering by price.
Then I’d like to join only the row with the lowest price from each group of flags

Answer 1

SELECT id, flag, price
FROM tbl t
WHERE NOT EXISTS (
  SELECT 1
  FROM tbl tt
  WHERE t.flag = tt.flag
    AND (tt.price < t.price 
         OR (tt.price = t.price AND t.id < tt.id)));

And here’s an sqlfiddle for it.