SQL性能-在联合之前或之后对查询进行过滤

Question

I have a query that looks like this:

SELECT PersonId,
       Note,
       Amount
FROM Table1 A
WHERE A.PersonId = @PersonId

UNION 

SELECT PersonId,
       Note,
       Amount
FROM Table2 B
WHERE B.PersonId = @PersonId

UNION 

SELECT PersonId,
       Note,
       Amount
FROM Table3 C
WHERE C.PersonId = @PersonId

Now, this query will eventually return thousands of results and so I want to build the best performing query possible. I want to know if that's more efficient than filtering on PersonId after the unions such as this:

SELECT * FROM 
(
SELECT PersonId,
       Note,
       Amount
FROM Table1 A

UNION 

SELECT PersonId,
       Note,
       Amount
FROM Table2 B

UNION 

SELECT PersonId,
       Note,
       Amount
FROM Table3 C
) A
WHERE A.PersonId = @PersonId

Answer 1

First at all you will have a query optimizer.
There will be no difference in speed, because the PersonId is on the display layer.
The query optimizer will change the execution order of the display parameters so that there will be a minimal amount of parameters.
So both queries will be equal at speed.
If you are interested, you can see this execution plan in your SQL developer.