Slow query with many joins - expanding the magic pill? - sql

Question

I have a query that takes 20 minutes to run, even though I have an index for every column in the where clauses, and every column being joined:
SELECT DISTINCT skt.VCDRAWING_REG_NO, skb.NDRAWING_ORG_NO, skb.NDRAWING_ORG_REV_NO, skb.CAPPLY_START_DATE, skb.CAPPLY_END_DATE, skto.*
FROM SPM_ABS_TRANBASE skt
JOIN SPM_ABS_BASE skb
ON skt.NDRAWING_ORG_REV_NO = skb.NDRAWING_ORG_REV_NO
AND skt.NDRAWING_ORG_NO = skb.NDRAWING_ORG_NO
JOIN SPM_ABS_MODEL skm
ON skb.NDRAWING_ORG_REV_NO = skm.NDRAWING_ORG_REV_NO
AND skb.NDRAWING_ORG_NO = skm.NDRAWING_ORG_NO
JOIN SPM_ABS_TRANOPT skto
ON skt.NDRAWING_SYSTEM_NO = skto.NDRAWING_SYSTEM_NO
JOIN ModelImport mi
ON skm.CMODEL = mi.ModelCode
WHERE (skb.CAPPLY_START_DATE <= DATEADD(day, 2, GETDATE()) OR skb.CAPPLY_START_DATE IS NULL)
AND (skb.CAPPLY_END_DATE >= DATEADD(day, -2, GETDATE()) OR skb.CAPPLY_END_DATE IS NULL)
Here is my query plan.
One thing that puzzles me is this: If I add the following WHERE clause, the query returns in about 0.5 seconds:
AND mi.ModelCode = '3FBK5'
Now you're saying, well, duh, of course it gets much faster with that - the thing is, the ModelImport table contains only 351 records. Which means if I were to split up the query above into 351 queries, each with its own where clause for a distinct ModelCode - then I can get 100% of my query results in about 175 seconds, or 2.9 minutes. This is dramatically faster. Which tells me that something in the wide-open query is grossly inefficient, and the query plan is bad.
Here is my query plan with AND mi.ModelCode = '3FBK5' added.
After viewing my query plan, any ideas how I can speed this up?

Answer 1

Is it possible that you eliminate some of the joins as you are not selecting anything from those tables or applying any where conditions to those tables, e.g., skm and mi?

Answer 2

Without having the table schema and sizes it's a little hard to give an exact answer, but here are some updates to try.
Use group by instead of distinct
Don't use * in the select results (particularly with distinct) instead give specific list of columns to return
Avoid "or" statements in where clause (maybe use ISNULL instead)
Here is what the query might look like with these updates (though there probably some other columns from skto you would want to add)
SELECT skt.VCDRAWING_REG_NO,
skb.NDRAWING_ORG_NO,
skb.NDRAWING_ORG_REV_NO,
skb.CAPPLY_START_DATE,
skb.CAPPLY_END_DATE,
skto.NDRAWING_SYSTEM_NO
FROM SPM_ABS_TRANBASE skt
JOIN SPM_ABS_BASE skb ON
skt.NDRAWING_ORG_REV_NO = skb.NDRAWING_ORG_REV_NO
AND skt.NDRAWING_ORG_NO = skb.NDRAWING_ORG_NO
JOIN SPM_ABS_MODEL skm ON
skb.NDRAWING_ORG_REV_NO = skm.NDRAWING_ORG_REV_NO
AND skb.NDRAWING_ORG_NO = skm.NDRAWING_ORG_NO
JOIN SPM_ABS_TRANOPT skto ON
skt.NDRAWING_SYSTEM_NO = skto.NDRAWING_SYSTEM_NO
JOIN ModelImport mi ON
skm.CMODEL = mi.ModelCode
WHERE ISNULL(skb.CAPPLY_START_DATE, DATEADD(day, 2, GETDATE())) <= DATEADD(day, 2, GETDATE())
AND ISNULL(skb.CAPPLY_END_DATE,DATEADD(day, -2, GETDATE())) >= DATEADD(day, -2, GETDATE())
GROUP BY skt.VCDRAWING_REG_NO,
skb.NDRAWING_ORG_NO,
skb.NDRAWING_ORG_REV_NO,
skb.CAPPLY_START_DATE,
skb.CAPPLY_END_DATE,
skto.NDRAWING_SYSTEM_NO