sql - 在 where 子句中使用计算字段

Question

有没有办法在where子句中使用计算字段？

我想做类似的事情

SELECT a, b, a+b as TOTAL FROM (
   select 7 as a, 8 as b FROM DUAL
   UNION ALL
   select 8 as a, 8 as b FROM DUAL
   UNION ALL
   select 0 as a, 0 as b FROM DUAL
)
WHERE TOTAL <> 0
;

但我明白了ORA-00904: "TOTAL": invalid identifier。

所以我必须使用

SELECT a, b, a+b as TOTAL FROM (
   select 7 as a, 8 as b FROM DUAL
   UNION ALL
   select 8 as a, 8 as b FROM DUAL
   UNION ALL
   select 0 as a, 0 as b FROM DUAL
)
WHERE a+b <> 0
;

Answer 1

从逻辑上讲，该select子句是评估查询的最后部分之一，因此别名和派生列不可用。（除了order by，逻辑上最后发生。）

使用派生表可以解决这个问题：

select * 
from (SELECT a, b, a+b as TOTAL FROM ( 
           select 7 as a, 8 as b FROM DUAL 
           UNION ALL 
           select 8 as a, 8 as b FROM DUAL 
           UNION ALL 
           select 0 as a, 0 as b FROM DUAL) 
    )
WHERE TOTAL <> 0 
; 

Answer 2

这将工作...

select * 
from (SELECT a, b, a+b as TOTAL FROM ( 
           select 7 as a, 8 as b FROM DUAL 
           UNION ALL 
           select 8 as a, 8 as b FROM DUAL 
           UNION ALL 
           select 0 as a, 0 as b FROM DUAL) 
    ) as Temp
WHERE TOTAL <> 0;