I'm using this query to get parents of a customer but it returns no result:
SELECT *
FROM (
SELECT
@r AS _id,
(SELECT @r := parent_id FROM data_customers_map_parents WHERE customer_id = _id) AS _pid,
@l := @l + 1 AS lvl
FROM
(SELECT @r := 1, @l := 0) vars,
data_customers_map_parents m
WHERE @r != null) T1
JOIN data_customers_map_parents T2
ON T1._id = T2.customer_id
ORDER BY T1.lvl DESC;
What's wrong with this query?