Will this UPDATE accomplish what I intend it to? - sql-server

Question

This is probably a very simple question for you SQL folks out there.
I have a temp table (TMP_VALIDATION_DATA) in which I've stored the old and new values of some fields I wish to update in a production table (PROVIDER_SERVICE), plus the uuids of the PROVIDER_SERVICE records that need to be updated.
What I want to accomplish is this, in pseudo-code:
For every prov_svc_uuid uuid in TMP_VALIDATION_DATA table
Set PROVIDER_SERVICE_RATE.END_DATE = NewPvSvcEndDate
Where [uuid in temp table] = [uuid in PROVIDER_SERVICE table]
end for
Is this Update statement going to accomplish what I need?
update PROVIDER_SERVICE
set END_DATE = (
select NewPvSvcEndDate
from TMP_VALIDATION_DATA T
where T.PROVIDER_SERVICE_UUID = PROVIDER_SERVICE.PROVIDER_SERVICE_UUID
)
If my UPDATE is incorrect, will you please provide the correction? Thanks.

Answer 1

Your query will update all records and you might get an error if you have more than one record in your subquery. I would also change your syntax to a JOIN similar to below.
update P
set END_DATE = T.NewPvSvcEndDate
FROM PROVIDER_SERVICE P
JOIN TMP_VALIDATION_DATA T
ON P.PROVIDER_SERVICE_UUID = T.PROVIDER_SERVICE_UUID
If you don't want to UPDATE all records, then add a WHERE clause.
My suggestion is if you don't know how many records would be included in the UPDATE, write your query as a SELECT first, then change it to an UPDATE. So for this one:
SELECT P.END_DATE, T.NewPvSvcEndDate
FROM PROVIDER_SERVICE P
JOIN TMP_VALIDATION_DATA T
ON P.PROVIDER_SERVICE_UUID = T.PROVIDER_SERVICE_UUID

Answer 2

This will either update all records, or error out (not sure what happens when you try to update a column with multiple values like that).