Question

我无法在计算列上写条件。我在Stackoverflow上看了几篇文章。不幸的是，我仍然无法弄明白。我有以下MySQL查询：

SELECT 
c.pk_tbl_commodity, c.s_name, c.s_default_variant,
p.pk_tbl_parameter, p.s_name_parameter,
((SELECT SUM(p2.n_price_parameter) from tbl_Parameter p2
        WHERE p2.fk_tbl_commodity = p.fk_tbl_commodity 
        AND p2.b_default = 1 
        AND p2.s_name_parameter <> p.s_name_parameter GROUP BY NULL) + c.n_price_without_dph + p.n_price_parameter) as total 
FROM tbl_Commodity c JOIN tbl_Parameter p on (p.fk_tbl_commodity = c.pk_tbl_commodity) 
WHERE s_name like '%acti%' 
AND b_bin = '0'
AND total = 3340
ORDER BY s_name, s_default_variant;

我收到了错误：

[Err] 1054 - Unknown column 'total' in 'where clause'

如何在子查询和sum（列别名 total ）的结果上添加条件？

谢谢。

Answer 1

SELECT列表中定义的别名无法在WHERE列表中引用，只是因为查询执行的（逻辑）顺序为FROM -> WHERE -> GROUP BY -> (HAVING) -> SELECT。

您可以尝试将AND total = 3340替换为HAVING total = 3340。

这不是标准的SQL，但它在MySQL中是允许的（它在执行HAVING和SELECT子句的顺序上是灵活的），并且可以避免重复{{{}中的代码。 1}}子句。

另一种方法是将查询封装在派生表中，并在外部WHERE子句中提取条件。

所以你的选择是：

使用WHERE（MySQL允许的技巧）：
```
HAVING
```
SELECT c.pk_tbl_commodity, c.s_name, c.s_default_variant, p.pk_tbl_parameter, p.s_name_parameter, (... long and complex subquery ...) AS total FROM tbl_Commodity c JOIN tbl_Parameter p on (p.fk_tbl_commodity = c.pk_tbl_commodity) WHERE s_name like '%acti%' AND b_bin = '0' HAVING total = 3340 ORDER BY s_name, s_default_variant ;和SELECT子句中的重复代码：
```
WHERE
```

封装在派生表中：

SELECT 
  c.pk_tbl_commodity, c.s_name, c.s_default_variant,
  p.pk_tbl_parameter, p.s_name_parameter,
  (... long and complex subquery ...) AS total 
FROM tbl_Commodity c JOIN tbl_Parameter p 
     on (p.fk_tbl_commodity = c.pk_tbl_commodity) 
WHERE s_name like '%acti%' 
  AND b_bin = '0'
  AND (... long and complex subquery ...) = 3340
ORDER BY s_name, s_default_variant ;

由于SELECT * FROM ( SELECT c.pk_tbl_commodity, c.s_name, c.s_default_variant, p.pk_tbl_parameter, p.s_name_parameter, (... long and complex subquery ...) AS total FROM tbl_Commodity c JOIN tbl_Parameter p on (p.fk_tbl_commodity = c.pk_tbl_commodity) WHERE s_name like '%acti%' AND b_bin = '0' ) AS dt WHERE total = 3340 ORDER BY s_name, s_default_variant ;列的结果不变（total），您也可以使用（不重复代码）：
```
3340
```

（如果条件是SELECT c.pk_tbl_commodity, c.s_name, c.s_default_variant, p.pk_tbl_parameter, p.s_name_parameter, 3340 AS total FROM tbl_Commodity c JOIN tbl_Parameter p on (p.fk_tbl_commodity = c.pk_tbl_commodity) WHERE s_name like '%acti%' AND b_bin = '0' AND (... long and complex subquery ...) = 3340 ORDER BY s_name, s_default_variant ;或者除了相等之外的任何其他条件，那当然不会起作用。）

在计算列（包括子查询）上使用子句WHERE

1 个答案: