Question

The SELECT statement below returns the correct data.

SELECT stu.sc, stu.sn, COUNT(*) AS Total,
    CASE
      WHEN COUNT(*) = 3 Then 'Letter 1'
      WHEN COUNT(*) = 4 Then 'Letter 2'
      WHEN COUNT(*) = 5 Then 'Letter 3'
      ELSE 'SARB'
    END AS Letter  
FROM STU  join att ON (stu.SC = att.SC and stu.SN = att.SN)
WHERE att.al in ('c','t','u')
GROUP by stu.sc, stu.sn
HAVING COUNT(*) >= 3

I need to perform an UPDATE based on that query, and I can’t seem to figure it out. I’ve looked at multiple examples online that are similar to what I need, but I can’t get this to work. I need to be able to do something like this…

UPDATE stu
SET stu.tru = 
   CASE
     When COUNT(*) = 3 Then 'Letter 1'
     When COUNT(*) = 4 Then 'Letter 2'
     When COUNT(*) = 5 Then 'Letter 3'
     ELSE 'SARB'
   END  
FROM stu  JOIN att
   on (stu.sc = att.sc and stu.sn = att.sn)
WHERE ATT.AL in ('c','t','u')
GROUP BY stu.sc, stu.sn
HAVING COUNT(*) >= 3

I know I can’t use Group By and Having in an Update statement directly, but I’ve seen examples where they use a Select with Group By before the Set and Join. I just can’t make it work.

Thanks for any help.

Answer 1

WITH CTE AS (
  SELECT stu.sc, stu.sn, COUNT(*) AS Total,
      CASE
        WHEN COUNT(*) = 3 Then 'Letter 1'
        WHEN COUNT(*) = 4 Then 'Letter 2'
        WHEN COUNT(*) = 5 Then 'Letter 3'
        ELSE 'SARB'
      END AS Letter  
  FROM STU  join att ON (stu.SC = att.SC and stu.SN = att.SN)
  WHERE att.al in ('c','t','u')
  GROUP by stu.sc, stu.sn
  HAVING COUNT(*) >= 3
)
UPDATE stu
SET stu.tru = cte.Letter
FROM stu  JOIN cte
   on (stu.sc = cte.sc and stu.sn = cte.sn)