如何在 SQL 的 where 子句中使用别名 [重复]答案

【问题标题】：how to use Alias Name in where clause in SQL [duplicate]如何在 SQL 的 where 子句中使用别名 [重复]
【发布时间】：2021-12-29 17:55:38
【问题描述】：

首先，我在这里查看了大部分答案，但我无法将解决方案应用于我的案例。它总是给我一个错误。

我需要在 where 子句中使用“FinalTotal”别名：

SELECT
        p.ID,
        p.TheName0, 

        (SELECT IFNULL(SUM(att.S_FinalAmount),0) From tbl_groups_classes_att att 
         INNER JOIN tbl_students st 
         ON st.ID = att.StudentID
         INNER JOIN tbl_groups_classes cls
         ON cls.ID = att.ClassID

         WHERE st.ParentID = p.ID 
        and cls.TheDate BETWEEN @Date1 and @Date2 
        and att.TheStatus <> 'N'
        ) as CurrMost,

        (SELECT IFNULL(SUM(att.S_FinalAmount),0) From tbl_groups_classes_att att 
         INNER JOIN tbl_students st 
         ON st.ID = att.StudentID
         INNER JOIN tbl_groups_classes cls
         ON cls.ID = att.ClassID

         WHERE st.ParentID = p.ID and cls.TheDate< @Date1 and att.TheStatus <> 'N'
        ) as PrevMost,

        (SELECT IFNULL(SUM(pay.TheAmount),0) From tbl_parents_payments pay Where p.ID = pay.ParentID
        AND pay.TheDate BETWEEN @Date1 and @Date2
        ) as CurrMadf,

        (SELECT IFNULL(SUM(pay.TheAmount),0) From tbl_parents_payments pay Where p.ID = pay.ParentID
        AND pay.TheDate < @Date1
        ) as PrevMadf,

        (SELECT CurrMost + PrevMost) as AllMost,
        (SELECT CurrMadf + PrevMadf) as AllMadf,
        (SELECT AllMost - AllMadf) AS FinalTotal 

        from tbl_parents p
        
        WHERE FinalTotal <> 0

但我得到了错误：

#1054 - Unknown column 'FinalTotal' in 'field list'

【问题讨论】：

只需将WHERE FinalTotal <> 0 替换为WHERE AllMost - AllMadf <> 0，并将(SELECT AllMost - AllMadf) 替换为AllMost - AllMadf ...
finalTotal column 在 WHERE 子句中不可用，因为（逻辑上）在创建列别名之前评估了 WHERE 子句。 MySQL 的特殊技巧是使用 HAVING 子句。

标签： mysql sql

【解决方案1】：

你应该使用子查询语法：

SELECT * FROM (
SELECT
    p.ID,
    p.TheName0, 

    (SELECT IFNULL(SUM(att.S_FinalAmount),0) From tbl_groups_classes_att att 
     INNER JOIN tbl_students st 
     ON st.ID = att.StudentID
     INNER JOIN tbl_groups_classes cls
     ON cls.ID = att.ClassID

     WHERE st.ParentID = p.ID 
    and cls.TheDate BETWEEN @Date1 and @Date2 
    and att.TheStatus <> 'N'
    ) as CurrMost,

    (SELECT IFNULL(SUM(att.S_FinalAmount),0) From tbl_groups_classes_att att 
     INNER JOIN tbl_students st 
     ON st.ID = att.StudentID
     INNER JOIN tbl_groups_classes cls
     ON cls.ID = att.ClassID

     WHERE st.ParentID = p.ID and cls.TheDate< @Date1 and att.TheStatus <> 'N'
    ) as PrevMost,

    (SELECT IFNULL(SUM(pay.TheAmount),0) From tbl_parents_payments pay Where p.ID = pay.ParentID
    AND pay.TheDate BETWEEN @Date1 and @Date2
    ) as CurrMadf,

    (SELECT IFNULL(SUM(pay.TheAmount),0) From tbl_parents_payments pay Where p.ID = pay.ParentID
    AND pay.TheDate < @Date1
    ) as PrevMadf,

    (SELECT CurrMost + PrevMost) as AllMost,
    (SELECT CurrMadf + PrevMadf) as AllMadf,
    (SELECT AllMost - AllMadf) AS FinalTotal 

    from tbl_parents p    
) as tab
 WHERE FinalTotal <> 0

【讨论】：

【解决方案2】：

这真的没有意义，因为没有GROUP BY

但是改变这个

WHERE FinalTotal <> 0

到这里

HAVING FinalTotal <> 0

简化测试

create table test (
id int auto_increment primary key, 
a int, 
b int
);

insert into test (a, b) values (1,1),(2,3);

select a, b
, a + b as ab
, (select ab + 10) as ab10
from test
having ab10 > 12;

a	b	ab	ab10
2	3	5	15

db小提琴here

【讨论】：