MySQL语句中的子查询问题

Question

我需要使用子查询来命名查询中的列。 我在SELECT部分编写了一个子查询语句，但是我收到以下错误消息（从Codeigniter返回）：

错误号码：1064

您的SQL语法有错误; 查看与您的MySQL服务器版本对应的手册，以便在'（SELECT ps_url_name FROM product_selects WHERE ps_id ='1'）附近使用正确的语法， psc_opt_2 A'在第1行

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'

文件名：models / products_model.php

行号：602

出了什么问题？

Answer 1

AS是列别名运算符，这意味着您将这些变量选为标识符。 您不能使用运算符来识别带有查询的变量。

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

相反，您需要反转使用别名运算符的方式，如下所示：

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'

理想情况下，您应该避免使用子查询（特别是在这种情况下）以避免表锁定开销。

Answer 2

格式正确

(SELECT `ps_url_name` FROM `product_selects` WHERE `ps_id` = '1') As `psc_opt_1` 

Answer 3

你试过这个：

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'

Answer 4

是否要将此列命名为psc_opt_1到psc_opt_1，或者您想要的是什么？

命名就像这样：

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'