sub-query question

From: Scott Frankel <leknarf(at)pacbell(dot)net>
To: pgsql-general(at)postgresql(dot)org
Subject: sub-query question
Date: 2004-11-12 17:52:09
Message-ID: 92D2847E-34D3-11D9-B6EE-000A95A7B782@pacbell.net
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-general


How does one embed a sub-query lookup to one table in order to
replace a foreign key id number with it's name in a SELECT on a
second table?

i.e.: given the following two tables, I want to replace the color_id
of 1
with the color_name 'red.' (The SQL to create the two tables follows
below.)

test=# SELECT * from users ;
color_id | name | the_date
----------+------+------------
1 | john | 2004-03-10
3 | jane | 2004-04-12
1 | joe | 2004-05-14
2 | jepe | 2004-06-16
(4 rows)

test=# SELECT * from colors;
color_id | color_name
----------+------------
1 | red
2 | green
3 | blue
(3 rows)

My attempts yield an 'f' which looks suspiciously like a boolean false.
Is there an ordering issue with my sub-query, such that the sub-query
doesn't have enough info to perform its lookup?

Here's my query:

SELECT (
u.color_id = (
SELECT c.color_name
FROM colors c
WHERE color_id = 1)) AS color_name,
u.name, u.the_date
FROM users u
WHERE u.color_id = 1
ORDER BY u.the_date DESC LIMIT 1;

It returns:

color_name | name | the_date
------------+------+------------
f | joe | 2004-05-14
(1 row)

Thanks!
Scott

Here's the SQL to create my test tables:

CREATE TABLE colors (color_id SERIAL PRIMARY KEY, color_name text);
CREATE TABLE users (color_id integer REFERENCES colors, name text,
the_date date);

INSERT INTO colors (color_name) VALUES ('red');
INSERT INTO colors (color_name) VALUES ('green');
INSERT INTO colors (color_name) VALUES ('blue');

INSERT INTO users (color_id, name, the_date) VALUES (1, 'john',
'2004-03-10');
INSERT INTO users (color_id, name, the_date) VALUES (3, 'jane',
'2004-04-12');
INSERT INTO users (color_id, name, the_date) VALUES (1, 'joe',
'2004-05-14');
INSERT INTO users (color_id, name, the_date) VALUES (2, 'jepe',
'2004-06-16');

Responses

Browse pgsql-general by date

  From Date Subject
Next Message Franco Bruno Borghesi 2004-11-12 18:22:08 Re: sub-query question
Previous Message Scott Chapman 2004-11-12 17:07:36 How to use custom functions created by my2pg.pl?