Question

I have the below select query I perform, however it is alarmingly slow against even ~6000 records and am curious if there is an alternate way to build the query?

select sum(Q.R) 
from (select 
        T.drawing_no,
        max(T.drawing_rev),
        T.R 
      from (select 
              drawing_no,
              drawing_rev,
              sum(price_total) as R 
            from data_pipe_drawing 
            where drawing_status="IP" 
            group by 
              drawing_no,
              drawing_rev) as T 
      group by T.drawing_no) as Q

In English the query finds all the drawings with a status of IP, rolls up the prices (price_total) by drawing_no+drawing_rev and then returns only the price_total of the highest revision for each drawing and rolls it all up for a grand price_total.

Thus before hitting the max(T.drawing_rev) if the query held:

 Drawing A Rev 1 Total Cost $100
 Drawing A Rev 0 Total Cost $50
 Drawing B Rev 0 Total Cost $200

The Drawing A Rev 0 is dropped from the grand total. The grand total is $300.

Hope this makes sense… thanks for any advice!

Answer 1

As per my comment, I don’t feel safe with the query you wrote, I’d do something with a correlated sub-query, like this…

  SELECT
--  drawing_no,
    SUM(price_total)
  FROM
    data_pipe_drawing AS data
  WHERE
    drawing_status="IP" 
    AND drawing_rev = (SELECT MAX(drawing_rev) FROM data_pipe_drawing WHERE drawing_status = "IP" AND drawing_no = data.drawing_no)
--GROUP BY
--  drawing_no

-- Commented lines useful for testing individual drawings

Then have an index on (drawing_status, drawing_no, drawing_rev)

Or possibly even this…

  SELECT
    SUM(data.price_total)
  FROM
    data_pipe_drawing AS data
  INNER JOIN
  (
    SELECT
      drawing_status,
      drawing_no,
      MAX(drawing_rev) AS drawing_rev
    FROM
      data_pipe_drawing
    GROUP BY
      drawing_status,
      drawing_no
  )
    AS lookup
      ON  lookup.drawing_number = data.drawing_number
      AND lookup.drawing_rev    = data.drawing_rev
      AND lookup.drawing_status = data.drawing_status
  WHERE
    data.drawing_status="IP" 

EDIT

Changed the JOIN based solution to possibly be friendlier for multiple drawing states, pending mor einfor from the OP.