Re: [GENERAL] sub-query question

[Scott Frankel]

Cooking with gas once again ;)  Thanks for the info on JOINs!
Scott

On Nov 12, 2004, at 9:52 AM, Scott Frankel wrote:
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');



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