Thanks. Since the number of conditions and the type of conditions (AND, OR ) etc are not known beforehand, I felt that generating the query as above (aliasing) may be a bit more difficult compared to generating a list of similar INTERSECTs or UNIONs. Since we have equijoins and and an exact match on skill, it should get executed fast? I got another way of doing this also.....
WHERE SKILL IN ('JAVA','ORACLE') group by student_id having count(*) = 2. If there are 3 skills, do a count(*)=3.
By the way, combination of student_id/skill will be unique in that table.
Any other ideas? I am collecting options - will check performance and use the best.
On Wed, Oct 9, 2013 at 8:12 PM, Kevin Grittner <kgrittn@ymail.com> wrote:
> from stud s > join stud_skill s_k on s.id = s_k.stud_id > join skill sk on sk.id = s_k.skill_id > where sk_name = 'Java' > intersect > select s.id, s.name > from stud s > join stud_skill s_k on s.id = s_k.stud_id > join skill sk on sk.id = s_k.skill_id
> where sk_name = 'Oracle' > ;
I think that in most (maybe all?) cases the set operations like INTERSECT cause the queries on both sides to be executed and the set operation performed on the results. It should be faster just to use two joins to the skill table:
