Re: showing multiple REFERENCE details of id fields in single

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