To get this poster, or any failing link you want to invest in getting, try this … take the failed URL trail “Logical-Query-Processing-Poster”
and internet search it for any other missing link yields you the below PDF

http://www.sql.co.il/books/insidetsql2008/Logical%20Query%20Processing%20Poster.pdf

I have a question on how the index order apears to be different than the logical processing order – but I need to read more on that before I ask.

Great information as always Itzik

Just Have a look at the following:

CREATE TABLE AA(PRODCODE CHAR(5),
RATE DECIMAL(20,2) NOT NULL DEFAULT 0,
LAST_REC CHAR(1) NOT NULL DEFAULT ”)

INSERT AA VALUES(‘P1′,25,’L')
INSERT AA VALUES(‘P1′,0,”)

SELECT * FROM AA

CREATE TABLE BB(PRODCODE CHAR(5),
RATE DECIMAL(20,2) NOT NULL DEFAULT 0)

INSERT BB VALUES(‘P1′,0)
INSERT BB VALUES(‘P2′,0)

UPDATE BB SET RATE=
ISNULL((SELECT TOP 1 1/RATE FROM AA WHERE AA.PRODCODE=BB.PRODCODE),0)
– It says (2 row(s) affected)
– If TOP would not have executed first then we naturally get
– a divide by zero error as in the next command
UPDATE BB SET RATE=
ISNULL((SELECT TOP 1 1/RATE FROM AA WHERE AA.PRODCODE=BB.PRODCODE ORDER BY RATE),0)
– Msg 8134, Level 16, State 1, Line 1
–Divide by zero error encountered.
–The statement has been terminated.

– Thus we may also conclude that the evaluation of Expressions and Column values in select statement is also restricted on TOP. Only TOP % or Number rows –column are retrieved or expressions are evaluated. Executing Order BY first than TOP would naturally lead to a divide by zero eror.