在 SQL 中对别名进行算术运算

Posted 2023-03-31

【中文标题】在 SQL 中对别名进行算术运算

【英文标题】：Doing arithmetic on alias in SQL

【发布时间】：2013-11-19 05:35:21

【问题描述】：

在我的 SQL 查询中，我需要对别名进行一些算术运算。

SELECT 
    MY_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME1, 
    MY_SECOND_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME2,  
    MYALIASNAME1 - MYALIASNAME2 AS MYALIASHNAME3
FROM 
    MYTABLE

但是，这不起作用，因为它没有将 MYALIASNAME1 和 MYALIASNAME2 视为列。任何想法我怎样才能做到这一点？

我正在使用 H2，特别是 h2-1.3.173.jar。我在服务器模式下使用它。

谢谢。

【问题讨论】：

***.com/questions/6081436/… 请看看这对你有什么意义。

请告诉我们这是什么具体的数据库系统 - 许多事情是特定于供应商的。你在使用 mysql 吗？后格雷斯？ SQL 服务器？甲骨文？ IBM DB2？完全不同的东西？请更新您的标签以显示您正在使用的数据库系统（以及它的哪个版本！） - 谢谢！

【参考方案1】：

试试这个。

SELECT X.MYALIASNAME1 - X.MYALIASNAME2 AS MYALIASNAME3 FROM
(
    SELECT 
        MY_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME1, 
        MY_SECOND_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME2

    FROM 
        MYTABLE
)X

【参考方案2】：

不要使用别名

SELECT 
   MY_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME1, 
   MY_SECOND_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME2,  
   MY_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN  - MY_SECOND_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASHNAME3
FROM 
    MYTABLE

或者使用中间步骤

SELECT MYALIASNAME1, MYALIASNAME2,  MYALIASNAME1 - MYALIASNAME2 AS MYALIASHNAME3
FROM  (

   SELECT 
       MY_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME1, 
       MY_SECOND_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME2
   FROM 
       MYTABLE
 ) TableAlias

【参考方案3】：

使用常用表表达式：

with cte as (
    select MY_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME1, 
        MY_SECOND_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME2
        
    from table
)
    
select MYALIASNAME1 - MYALIASNAME2 AS MYALIASHNAME3 from cte

【参考方案4】：

它会起作用的......

"SELECT 
    MY_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME1, 
    MY_SECOND_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN AS MYALIASNAME2,  
    (MY_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN) - (MY_SECOND_COMPLEX_EXPRESSION_USING_SUM_AND_CASEWHEN) AS MYALIASHNAME3
FROM 
    MYTABLE"