Question

SELECT * 
FROM   sec 
WHERE  sec.cu IN (SELECT s.cu 
                  FROM   sec s WITH (nolock) 
                  WHERE  EXISTS (SELECT * 
                                 FROM   hact h WITH ( nolock), 
                                 JOIN   dport p WITH ( nolock) ON h.ic = p.ic
                                 WHERE  s.cu = h.cu )

                  UNION 
                  SELECT s.cu 
                  FROM   sec s WITH (nolock) 
                  WHERE  EXISTS(SELECT * 
                                FROM   schanges c WITH ( nolock) 
                                WHERE  s.cu = c.cu) 
                  UNION 
                  SELECT s.cu 
                  FROM   sec s WITH (nolock) 
                  WHERE  s.cu IN (SELECT DISTINCT cu 
                                  FROM   suk WITH (nolock))) 
       AND EXISTS (SELECT * 
                   FROM   hact h WITH (nolock) 
                          JOIN port p WITH (nolock) 
                            ON h.ic = p.ic 
                   WHERE  sec.cu = h.cu 
                          AND p.ptype = 'X') 

Hi I have this query which i am trying to optimize. I have tries to convert it to remove unions and In to more readable but failed. I am trying to make it more efficient probably only using EXISTS and NOT EXISTS.

Answer 1

Here’s a simplified version that should be functionally equivalent:

SELECT s.*
FROM   sec s WITH (nolock) 
WHERE (
  EXISTS (
    SELECT * 
    FROM   hact h WITH ( nolock)
    JOIN   dport p WITH ( nolock) 
      ON h.ic = p.ic
    WHERE  s.cu = h.cu 
  ) OR EXISTS (
    SELECT * 
    FROM   schanges c WITH ( nolock)
    WHERE  s.cu = c.cu
  ) OR EXISTS (
    SELECT *
    FROM   suk WITH (nolock)
    WHERE  s.cu = suk.cu
  )
) AND EXISTS (
  SELECT * 
  FROM   hact h WITH (nolock) 
  JOIN port p WITH (nolock) 
    ON h.ic = p.ic 
  WHERE  
    s.cu = h.cu 
    AND p.ptype = 'X'
)