sql-server - SQL Server CTE 隐式列数据类型问题

Question

我在使用 SQL Server 公用表表达式 (CTE) 时遇到了一个非常奇怪的错误。

我认为通过给出代码示例来解释我的问题是最容易的。

CREATE TABLE #Test1 (TestCol varchar(3));

INSERT INTO #Test1 VALUES ('012')
INSERT INTO #Test1 VALUES ('ABC')

--This simple shows the Cast works as expected, and only on rows where the TestCol value is numeric
SELECT TestCol, CAST(TestCol as int) as IntCast 
FROM #Test1 
WHERE ISNUMERIC(TestCol) = 1;

--Here I create a cte using the same SQL as show above.
with cte as (
    SELECT 
       TestCol, CAST(TestCol as int) as IntCast 
    FROM #Test1 
    WHERE ISNUMERIC(TestCol) = 1
)

/*
I have two examples below. The first can be executed to check for the existence of our 'ABC' value.  It doesn't show up, which is expected. 
The Second example, simple checks to see if our IntCast column is greater than 10.  This throws an exception
*/

--SELECT * FROM cte
SELECT * FROM cte WHERE IntCast > 10

DROP TABLE #Test1

这里的例外是

将 varchar 值“ABC”转换为数据类型 int 时转换失败

我很好奇这是在哪里发生的？

Answer 1

with cte as (
    SELECT TestCol, Case when ISNUMERIC(TestCol) = 1 then CAST(TestCol as int) else NULL end as IntCast FROM #Test1  
)