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
SELECT
a.id AS class_id,
c.id AS prerequisite_class
FROM
classes a
JOIN class_prerequisite_bindings b ON b.class_id = a.id
JOIN classes c ON c.id = b.prerequisite
WHERE
a.id = 1;
go
Ferindo
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--
Daryl
"We want great men who, when fortune frowns, will not be discouraged."
-- Colonel Henry Knox, 1776
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