Question

I need to use subqueries to name columns in a query. I have written a statement with subqueries in the SELECT section, but I am getting the following error message (returned from Codeigniter):

Error Number: 1064

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘(SELECT ps_url_name FROM product_selects WHERE ps_id = ‘1’), psc_opt_2 A’ at line 1

SELECT
    `psc_opt_1` AS (SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '1'),
    `psc_opt_2` AS (SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '2'),
    `psc_opt_3` AS (SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '3'),
    `psc_opt_4` AS (SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '4'),
    `psc_opt_5` AS (SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '5')
FROM (`product_stock_control`)
WHERE `psc_prod_id` = '5'

Filename: models/products_model.php

Line Number: 602

Any ideas what is going wrong?

Answer 1

AS is a column alias operator, meaning you are selecting these variables as an identifier. You cannot use the operator to identify a variable with a query.

Reference: http://dev.mysql.com/doc/refman/5.0/en/problems-with-alias.html

Instead, you’ll need to reverse how you use the alias operator like so:

SELECT
    (SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '1') AS `psc_opt_1`,
    (SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '2') AS `psc_opt_2`,
    (SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '3') AS `psc_opt_3`,
    (SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '4') AS `psc_opt_4`,
    (SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '5') AS `psc_opt_5`
FROM (`product_stock_control`)
WHERE `psc_prod_id` = '5'

Ideally, you should avoid using subqueries (especially in this case) to avoid table-locking overhead.