Hi Chris,
Here is my attempt doing this with a rCTE
;WITH retained AS (
SELECT t.retained, dropped
FROM testing t
WHERE NOT EXISTS (SELECT 1 FROM testing i WHERE i.dropped = t.retained)
UNION ALL
SELECT b.retained, t1.dropped
FROM testing AS t1
INNER JOIN retained as b
ON t1.retained = b.dropped)
UPDATE t
SET t.retained = uv.retained
FROM testing t
INNER JOIN retained uv
ON t.dropped = uv.dropped
This works with the sample data but something isn't quite right with this. Tried it with a sample of 160000 records, it took 17 seconds.
When I increased the sample record set to 200000, the query just keeps going. It's scaling up badly or there's some dodgy data that the above logic just can't handle efficiently.
This is what the estimated execution plan is telling me:
Tried adding a couple of indexes on retained and dropped columns but that made no difference to the estimated execution plan.
Arrrggghhh! :w00t:
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