Which SQL query is faster? Filter on Join criteria or Where clause?

Question

Compare these 2 queries. Is it faster to put the filter on the join criteria or in the WHERE clause. I have always felt that it is faster on the join criteria b

Answer 1

Performance-wise, they are the same (and produce the same plans)

Logically, you should make the operation that still has sense if you replace INNER JOIN with a LEFT JOIN.

In your very case this will look like this:

SELECT  *
FROM    TableA a
LEFT JOIN
        TableXRef x
ON      x.TableAID = a.ID
        AND a.ID = 1
LEFT JOIN
        TableB b
ON      x.TableBID = b.ID

or this:

SELECT  *
FROM    TableA a
LEFT JOIN
        TableXRef x
ON      x.TableAID = a.ID
LEFT JOIN
        TableB b
ON      b.id = x.TableBID
WHERE   a.id = 1

The former query will not return any actual matches for a.id other than 1, so the latter syntax (with WHERE) is logically more consistent.