sql - 从查询结果创建一个 sql 变量以在同一查询中使用

Question

我想做以下查询：

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

但是，我似乎无法弄清楚如何放入CHARINDEX('X', violations, 0)一个变量 ( VarX) 中，所以我最终得到了类似的东西：

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

我这样做是为了避免两次运行 CHARINDEX。

Answer 1

尝试：

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

为了便于说明和减少打字，可以（尽管大多数人可能会对此皱眉）：

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

假设 SQL Server 2005+，您可以使用 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;