在 WHERE 子句中使用子查询结果列时的未知列 [英] Unknown column when using subquery result column in WHERE clause

问题描述

我要加入几个表，以便使用 COUNT() 选择总计列.此查询非常适合返回 total 列:

I have a few tables I'm joining to select a column for totals using COUNT(). This query works great with returning the total column:

SELECT *,`excel`.`drivers`.`AutoNumber` AS `current_driver`,
(SELECT COUNT(`issues`.`categories`.`points`) FROM `issues`.`points` INNER JOIN `excel`.`drivers` ON `issues`.`points`.`driver_id` = `excel`.`drivers`.`AutoNumber` INNER JOIN `issues`.`categories` ON `issues`.`categories`.`id` = `issues`.`points`.`category_id` WHERE `excel`.`drivers`.`AutoNumber`=`current_driver`) AS `total` 
FROM `issues`.`points` 
INNER JOIN `excel`.`drivers` ON `issues`.`points`.`driver_id` = `excel`.`drivers`.`AutoNumber` 
INNER JOIN `issues`.`categories` ON `issues`.`categories`.`id` = `issues`.`points`.`category_id`

但现在我正在尝试创建一个查询来比较 WHERE 子句中的 total，如下所示:

But now I'm trying to create a query that compares total in there WHERE clause, like this:

SELECT *,`excel`.`drivers`.`AutoNumber` AS `current_driver`,
(SELECT COUNT(`issues`.`categories`.`points`) FROM `issues`.`points` INNER JOIN `excel`.`drivers` ON `issues`.`points`.`driver_id` = `excel`.`drivers`.`AutoNumber` INNER JOIN `issues`.`categories` ON `issues`.`categories`.`id` = `issues`.`points`.`category_id` WHERE `excel`.`drivers`.`AutoNumber`=`current_driver`) AS `total` 
FROM `issues`.`points` 
INNER JOIN `excel`.`drivers` ON `issues`.`points`.`driver_id` = `excel`.`drivers`.`AutoNumber` 
INNER JOIN `issues`.`categories` ON `issues`.`categories`.`id` = `issues`.`points`.`category_id` WHERE `total` = 3

这会返回一个错误，指出 total 是一个未知列.有什么想法吗?

This returns with an error that total is an unknown column. Any ideas?

推荐答案

列别名不能在 WHERE 子句中使用.试试

Column aliases cannot be used in WHERE clause. Try

select a.* 
FROM 
(
SELECT [column_list]
,`excel`.`drivers`.`AutoNumber` AS `current_driver`,
(SELECT COUNT(`issues`.`categories`.`points`) FROM `issues`.`points` INNER JOIN `excel`.`drivers` ON `issues`.`points`.`driver_id` = `excel`.`drivers`.`AutoNumber` INNER JOIN `issues`.`categories` ON `issues`.`categories`.`id` = `issues`.`points`.`category_id` WHERE `excel`.`drivers`.`AutoNumber`=`current_driver`) AS `total` 
FROM `issues`.`points` 
INNER JOIN `excel`.`drivers` ON `issues`.`points`.`driver_id` = `excel`.`drivers`.`AutoNumber` 
INNER JOIN `issues`.`categories` ON `issues`.`categories`.`id` = `issues`.`points`.`category_id`
)a 
WHERE a.`total` >3

您也可以在 WHERE 中重复total"的整个定义 - 智能优化器很可能会生成相同的计划，但为了可读性我不会这样做.

You can also repeat the whole definition of "total" in WHERE - smart optimizer will very likely generate the same plan, but I wouldn't do that for readability sake.

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