When should I use CROSS APPLY over INNER JOIN?

Can anyone give me a good example of when CROSS APPLY makes a difference in those cases where INNER JOIN will work as well?

See the article in my blog for detailed performance comparison:

• INNER JOIN vs. CROSS APPLY

CROSS APPLY works better on things that have no simple JOIN condition.

This one selects 3 last records from t2 for each record from t1:

SELECT  t1.*, t2o.*
FROM    t1
CROSS APPLY
        (
        SELECT  TOP 3 *
        FROM    t2
        WHERE   t2.t1_id = t1.id
        ORDER BY
                t2.rank DESC
        ) t2o

It cannot be easily formulated with an INNER JOIN condition.

You could probably do something like that using CTE‘s and window function:

WITH    t2o AS
        (
        SELECT  t2.*, ROW_NUMBER() OVER (PARTITION BY t1_id ORDER BY rank) AS rn
        FROM    t2
        )
SELECT  t1.*, t2o.*
FROM    t1
INNER JOIN
        t2o
ON      t2o.t1_id = t1.id
        AND t2o.rn <= 3

, but this is less readable and probably less efficient.

Update:

Just checked.

master is a table of about 20,000,000 records with a PRIMARY KEY on id.

This query:

WITH    q AS
        (
        SELECT  *, ROW_NUMBER() OVER (ORDER BY id) AS rn
        FROM    master
        ),
        t AS 
        (
        SELECT  1 AS id
        UNION ALL
        SELECT  2
        )
SELECT  *
FROM    t
JOIN    q
ON      q.rn <= t.id

runs for almost 30 seconds, while this one:

WITH    t AS 
        (
        SELECT  1 AS id
        UNION ALL
        SELECT  2
        )
SELECT  *
FROM    t
CROSS APPLY
        (
        SELECT  TOP (t.id) m.*
        FROM    master m
        ORDER BY
                id
        ) q

is instant.