Cartesian product and WHERE clause issue - sql

Question

Let us have simple table:
CREATE TABLE dbo.test
(
c1 INT
)
INSERT INTO test (c1) VALUES (1)
INSERT INTO test (c1) VALUES (2)
INSERT INTO test (c1) VALUES (3)
Next calculate some SUM:
SELECT SUM(t1.c1) FROM test AS t1 , test AS t2
WHERE t2.c1 = 1
Output is: 6 . Simple and easy.
But if I run:
SELECT SUM(t1.c1), * FROM test AS t1 , test AS t2
WHERE t2.c1 = 1
The output is:
6 2 2
6 2 3
6 2 1
6 3 2
6 3 3
6 3 1
6 1 2
6 1 3
6 1 1
My question is: Why the second output is not matching the condition in WHERE clause?

Answer 1

Looks like Sybase implements it's own extensions to GROUP BY:
Through the following extensions, Sybase lifts restrictions on what
you can include or omit in the select list of a query that includes
group by.
The columns in the select list are not limited to the grouping columns
and columns used with the vector aggregates.
The columns specified by group by are not limited to those
non-aggregate columns in the select list.
However, the results of the extension are not always intuitive:
When you use the Transact-SQL extensions in complex queries that
include the where clause or joins, the results may become even more
difficult to understand.
How does this relate to your problem?
However, the way that Adaptive Server handles extra columns in the
select list and the where clause may seem contradictory. For example:
select type, advance, avg(price)
from titles
where advance > 5000
group by type
type advance
------------- --------- --------
business 5,000.00 2.99
business 5,000.00 2.99
business 10,125.00 2.99
business 5,000.00 2.99
mod_cook 0.00 2.99
mod_cook 15,000.00 2.99
popular_comp 7,000.00 21.48
popular_comp 8,000.00 21.48
popular_comp NULL 21.48
psychology 7,000.00 14.30
psychology 2,275.00 14.30
psychology 6,000.00 14.30
psychology 2,000.00 14.30
psychology 4,000.00 14.30
trad_cook 7,000.00 17.97
trad_cook 4,000.00 17.97
trad_cook 8,000.00 17.97
(17 rows affected)
It only seems as if the query is ignoring the where clause when you
look at the results for the advance (extended) column. Adaptive Server
still computes the vector aggregate using only those rows that satisfy
the where clause, but it also displays all rows for any extended
columns that you include in the select list. To further restrict these
rows from the results, you must use a having clause.
So, to give you the results you would expect, Sybase should allow you to do:
SELECT SUM(t1.c1), * FROM test AS t1 , test AS t2
WHERE t2.c1 = 1
HAVING t2.c1 = 1
The WHERE will exclude the results from the total SUM; the HAVING will hide records that don't match the condition.
Confusing, isn't it?
Instead, you'd probably be better off writing the query so that it doesn't require Sybase's GROUP BY extensions.