SQL Join does not join

Question

Hi everyone,
I have a little issue with an SQL statement. I have found a problem to my query and it's just because I want to understand that I post...
i would like to transform this query to the same using ANSI syntax (outer joins) but I don't find the solution.
SELECT pa.user_id,
       pa.nom_complet_np,
       pa.organisation,
       pa.directory,
       group_2.i_supergroups_names
FROM pa pa
     INNER JOIN user user ON (pa.user_id = user.user_name)
     LEFT OUTER JOIN group group_r_1 ON (group_r_1.users_names = user.user_name)
     INNER JOIN group group_2 ON (group_2.object_id = group_r_1.object_id
                                AND group_2.i_supergroups_names = 'profile')
WHERE directory = 'MAIN'
  AND user.usertate = 0
ORDER BY user_id;The previous query does not return the correct value.
SELECT pa.user_id,
       pa.nom_complet_np,
       pa.organisation,
       pa.directory,
       (SELECT DISTINCT gr2.i_supergroups_names as group_name
FROM group gr1
     INNER JOIN group gr2 ON (gr2.object_id = gr1.object_id
                                            AND gr2.i_supergroups_names is not NULL)
WHERE gr1.users_names = user.user_name
  AND gr2.i_supergroups_names = 'profile')     
FROM hermcomp_ref.pa pa
     INNER JOIN user user ON (pa.user_id = user.user_name)
WHERE DG = 'MAIN'
  AND user.usertate = 0
ORDER BY user_id;But this one, does. But it's the same one using a SELECT instead of a JOIN... So I'm a little confused and I don't understand! Can anyone tell me where I'm wrong?
Thanks,

Answer 1

user13117585 wrote:
Thanks Sven, but can you tell me what is the differences between the 2 queries I did. They should be the same. No?No.
Didn't you notice that yourself?
user13117585 wrote:
The previous query does not return the correct value.
But this one, does. That proves they are not equivalent.
The query that produces the results you want does the self-join on group first, then the results are incoprporated into the other results as a scalar sub-query in the SELECT clause. Nothing that goes on in the SELECT clause can change the number of rows in the result set.
The query that does not get the results you want does an outer-join with one copy of group, and then does an inner join with the other copy of group. An inner join can change the number of rows in the result set.
Whether you do the inner join or the outer join first does matter, just like it matters whether you do the addition or the multiplication first in
2 + 1 * 0 
By the way, GROUP and USER and not good names for tables. Make up names that are not already keywords in Oracle, or built-in functions. Names that end in "_tbl" (e.g., group_tbl and user_tbl) should be okay.