mysql - 在计算列(包括子查询)上使用 WHERE 子句

Question

我无法在计算列上写入条件。我读过几篇关于 Stackoverflow 的文章。不幸的是，我仍然无法弄清楚。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;

我得到了错误:

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

如何在子查询和求和(列别名 total)的结果上添加条件？

谢谢。

Answer 1

在 SELECT 列表中定义的别名不能在 WHERE 列表中引用，因为查询的(逻辑)执行顺序是 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 HAVING 和 SELECT 子句的执行顺序上是灵活的)并且可以避免重复WHERE 子句中的代码。

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 HAVING(MySQL 允许的技巧):

  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 ;
  

• SELECT 和 WHERE 子句中的重复代码:

  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 ;
  

• 封装在派生表中:

  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 ;
  

---

• 由于 total 列将有一个常量结果 (3340)，您还可以使用(无重复代码):

  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 ;
  

(如果条件是 >= 3340 或除相等之外的任何其他条件，那当然不会起作用。)