SQL Query Performance Issues Using Subquery - sql

Question

I am having issues with my query run time. I want the query to automatically pull the max id for a column because the table is indexed off of that column. If i punch in the number manually, it runs in seconds, but i want the query to be more dynamic if possible.
I've tried placing the sub-query in different places with no luck
SELECT *
FROM TABLE A
JOIN TABLE B
ON A.SLD_MENU_ITM_ID = B.SLD_MENU_ITM_ID
AND B.ACTV_FLG = 1
WHERE A.WK_END_THU_ID_NU >= (SELECT DISTINCT MAX (WK_END_THU_ID_NU) FROM TABLE A)
AND A.WK_END_THU_END_YR_NU = YEAR(GETDATE())
AND A.LGCY_NATL_STR_NU IN (7731)
AND B.SLD_MENU_ITM_ID = 4314
I just want this to run faster. Maybe there is a different approach i should be taking?

Answer 1

I would move the subquery to the FROM clause and change the WHERE clause to only refer to A:
SELECT *
FROM A CROSS JOIN
(SELECT MAX(WK_END_THU_ID_NU) as max_wet
FROM A
) am
ON a.WK_END_THU_ID_NU = max_wet JOIN
B
ON A.SLD_MENU_ITM_ID = B.SLD_MENU_ITM_ID AND
B.ACTV_FLG = 1
WHERE A.WK_END_THU_END_YR_NU = YEAR(GETDATE()) AND
A.LGCY_NATL_STR_NU IN (7731) AND
A.SLD_MENU_ITM_ID = 4314; -- is the same as B
Then you want indexes. I'm pretty sure you want indexes on:
A(SLD_MENU_ITM_ID, WK_END_THU_END_YR_NU, LGCY_NATL_STR_NU, SLD_MENU_ITM_ID)
B(SLD_MENU_ITM_ID, ACTV_FLG)
I will note that moving the subquery to the FROM clause probably does not affect performance, because SQL Server is smart enough to only execute it once. However, I prefer table references in the FROM clause when reasonable. I don't think a window function would actually help in this case.