創建從查詢結果中的SQL變量在同一個查詢中使用

Question

我想要做以下查詢：

SELECT SUBSTRING(violations, CHARINDEX('X', violations, 0), 5) AS 'violations', definition, value, date 
FROM NewViolations WHERE CHARINDEX('X', violations, 0) > 0 

不過，我似乎無法弄清楚如何把CHARINDEX('X', violations, 0)成變量（VarX），使我最終是這樣的：

SELECT SUBSTRING(violations, VarX, 5) AS 'violations', definition, value, date 
FROM NewViolations WHERE VarX > 0 

我這樣做是爲了避免運行CHARINDEX兩次。

Answer 1

嘗試：

select substring(violations, location, 5) as 'violations', definition, value, date 
from (select violations, charindex('x',violations,0) location, definition, value, date 
     from NewViolations) a 
where a.location>0 

爲了說明的緣故，有點少打字，人們可以（雖然大部分可能會皺眉吧）：

select substring(violations, location, 5) as 'violations', definition, value, date 
from (select *, charindex('x',violations,0) location 
     from NewViolations) a 
where a.location>0 

Answer 2

假設的SQL Server 2005 +，你可以使用CTE：

WITH cteCharIndex AS (
    SELECT violations, CHARINDEX('X', violations, 0) AS PosOfX 
     FROM NewViolations 
) 
SELECT SUBSTRING(violations, PosOfX, 5) AS 'violations' 
    FROM cteCharIndex 
    WHERE PosOfX > 0;