Ferindo Middleton Jr wrote:
> I have a table which has two id fields which REFERENCE data back at
> another table. It's setup like this:
>
> class_prerequisite_bindings(id SERIAL, class_id INTEGER REFERENCES
> classes(id), prerequisite INTEGER REFERENCES classes(id))
>
> The classes table is like this:
> classes(id SERIAL, course_title TEXT, course_code TEXT)
>
> I have the following query:
> SELECT * FROM class_prerequisite_bindings, classes WHERE
> class_prerequisite_bindings.class_id = 64 AND
> class_prerequisite_bindings.class_id = classes.id;
>
> If I run the query above, the result will only give me info about the
> class_id field matching id 64 back in the classes table. PROBLEM: I want
> this query to also show the info about the prerequisite field which
> would also have info at the classes table. This query will only show the
> course_title and course_code of the class_id but I need this for the
> prerequisite field as well. I think I need to do a JOIN, but I don't
> understand how. How can I do this?
>
create table classes( id SERIAL PRIMARY KEY, course_title TEXT, course_code
TEXT );
go
insert into classes( course_title, course_code ) values( 'A', 'A1' );
insert into classes( course_title, course_code ) values( 'B', 'B1' );
insert into classes( course_title, course_code ) values( 'C', 'C1' );
go
create table class_prerequisite_bindings( id SERIAL, class_id INTEGER REFERENCES classes(id),
prerequisite INTEGER REFERENCES classes(id)
);
go
insert into class_prerequisite_bindings( class_id, prerequisite )
values( 1, 2 );
insert into class_prerequisite_bindings( class_id, prerequisite )
values( 1, 3 );
go
SELECTa.id AS class_id,c.id AS prerequisite_class
FROMclasses a
JOIN class_prerequisite_bindings b ON b.class_id = a.id
JOIN classes c ON c.id = b.prerequisite
WHEREa.id = 1;
go
> Ferindo
>
> ---------------------------(end of broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings
--
Daryl
"We want great men who, when fortune frowns, will not be discouraged." -- Colonel Henry Knox, 1776
