SQL UPDATE order of evaluation

Question

What is the order of evaluation in the following query:

UPDATE tbl SET q = q + 1, p = q;

That is, will \"tbl\".\"p\" be set to

Answer 1

The UPDATE does not see the results of its work.

p will be set to q as of before update.

The following code will just swap the columns:

DECLARE @test TABLE (p INT, q INT)

INSERT
INTO    @test
VALUES  (2, 3)

SELECT  *
FROM    @test

p    q
---  ---
  2    3

UPDATE  @test
SET     p = q,
        q = p

SELECT  *
FROM    @test

p    q
---  ---
  3    2