Sql 不能在CTE中浇铸

我很好奇，为什么我在像这样转换“tmp”数据项时会出现语法错误

考虑到这是可行的，但会由于数据类型不匹配而出现错误：

;WITH tmp(date, dataitem , data) AS 
(
    SELECT 
        date, LEFT(msg, CHARINDEX(';', msg + ';') - 1),  
        STUFF(msg, 1, CHARINDEX(';', msg + ';'), '')   
    FROM
        DB1 
    WHERE
        action LIKE 'FILE UPLOAD FTP' 
        AND date BETWEEN '06/01/2016' AND '07/05/2017'

    UNION ALL

    SELECT 
        date,  CHARINDEX(';', data + ';'),  
        STUFF(data, 1, CHARINDEX(';', Data + ';'), '') 
    FROM
        tmp 
    WHERE
        data > ''
)
SELECT 
    date, dataitem, 
    REPLACE(SUBSTRING(dataitem, 1, CHARINDEX('|', dataitem) - 1), 'FTP UPLOAD: ', '') AS orig_file_name, 
    SUBSTRING(dataitem, CHARINDEX('|', dataitem) + 1, 8000) AS file_name,
    (SELECT TOP 1 counts FROM DB1 
     WHERE action LIKE 'FILTER' 
       AND date> tmp.date 
       AND msg LIKE SUBSTRING(tmp.dataitem, CHARINDEX('|', dataitem ) + 1, 8000) + '%' 
     ORDER BY date) AS filter_counts,
FROM
    tmp
ORDER BY 
    date

---

当然，您可以在CTE中使用

CAST

，仅在

选择列表中使用，而不在列列表中使用：

WITH tmp(date, dataitem , data) AS (
     SELECT date, 
            CAST (LEFT(msg, CHARINDEX(';',msg+';')-1) AS VARCHAR(255)),  
            STUFF(msg, 1, CHARINDEX(';',msg+';'), '')   
     FROM DB1
     ...

因为列名就是这样；名字。它们不会像您在查询定义中那样定义结构和类型。注意：只有在查询定义中提供了所有结果列的不同名称时，列名列表才是可选的。
WITH tmp(date, dataitem , data) AS (
     SELECT date, 
            CAST (LEFT(msg, CHARINDEX(';',msg+';')-1) AS VARCHAR(255)),  
            STUFF(msg, 1, CHARINDEX(';',msg+';'), '')   
     FROM DB1
     ...