How to use outer query's columns in subqueries?

Question

I have a table with inventory records and another table with documents describing each inventory records, something like:

inventory (t1)
t1id        t1c1
1          desc1
2          desc2
3          desc3

documents (t2)
t2id    t2c1     t1id
1       doc1     1
2       doc2     1
3       doc3     2
4       doc4     3

so i try this query an I get an error telling me that there is no such column (t1.t1id) near the sub query =s

SELECT t1c1,(SELECT GROUP_CONCAT(t2c1) FROM t2 WHERE t1.t1id = t2.t1id) FROM t1

any Ideas?

Answer 1

You have to specify the table names (documents, inventory)

SELECT t1c1,  (SELECT GROUP_CONCAT(t2c1) 
               FROM documents t2 
               WHERE t1.t1id = t2.t1id) 
FROM inventory t1

Answer 2

This works on both 5.0 and 5.1:

CREATE TABLE t1 (t1id INT NOT NULL, t1c1 VARCHAR(20) NOT NULL);

CREATE TABLE t2 (t2id INT NOT NULL, t2c1 INT NOT NULL, t1id INT NOT NULL);

SELECT  t1c1,
        (
        SELECT  GROUP_CONCAT(t2c1)
        FROM    t2
        WHERE   t1.t1id = t2.t1id
        )
FROM    t1

You may try rewriting it as a JOIN:

SELECT  t1c1, GROUP_CONCAT(t2c1)
FROM    t1
LEFT JOIN
        t2
ON      t2.t1id = t1.t1id
GROUP BY
        t1.t1id