将 varchar 值转换为 int 时出现错误转换失败

Question

我的代码出现以下错误：

转换 varchar 值时转换失败 '(CASE WHEN ROW_NUM = ' 到数据类型 int。

我做错了什么？

DECLARE @N          INT = 6, 
        @I          INT = 0, 
        @SQL        NVARCHAR(MAX) 


BEGIN
 SET @SQL = '(CASE WHEN ROW_NUM = '+@I+'THEN problem ELSE NULL END) ';
 SET @I = @I+1;
END

EXEC SP_EXECUTESQL 
  @SQL 

Answer 1

仅根据您发布的代码，您缺少 SELECT 语句和 FROM 子句。您还假设您有一个名为 ROW_NUM 的列和一个名为 problem 的列：

DECLARE @N          INT = 6, 
        @I          INT = 0, 
        @SQL        NVARCHAR(MAX) 


BEGIN

  SET @SQL = 'SELECT CASE WHEN ROW_NUM = '+CAST(@I as VARCHAR(10))+' 
  THEN problem ELSE NULL END FROM MyTable';
 SET @I = @I+1;

END
print @SQL
EXEC SP_EXECUTESQL @SQL 

但是，您似乎也在尝试执行 WHILE 循环而不实际定义 WHILE，您可以这样做：

DECLARE @N          INT = 6, 
        @I          INT = 0, 
        @SQL        NVARCHAR(MAX) 

WHILE @I <= @N   -- new code

 BEGIN
  SET @SQL = 'SELECT CASE WHEN ROW_NUM = '+CAST(@I as VARCHAR(10))+' THEN problem ELSE NULL END FROM MyTable';
  SET @I = @I+1;
  PRINT @SQL
  EXEC SP_EXECUTESQL @SQL 
 END

我认为您实际上正在寻找这样的东西：

SELECT 'Problem', *
FROM (SELECT *, ROW_NUMBER() OVER (ORDER BY ROW_NUM) rn FROM MyTable) s
WHERE rn <> ROW_NUM

带有虚拟数据的示例：

DECLARE @MyTable TABLE (ROW_NUM INT, SomeData VARCHAR(5))
INSERT INTO @MyTable (ROW_NUM, SomeData) VALUES (1, 'foo')
INSERT INTO @MyTable (ROW_NUM, SomeData) VALUES (2, 'zip')
INSERT INTO @MyTable (ROW_NUM, SomeData) VALUES (3, 'yak')
INSERT INTO @MyTable (ROW_NUM, SomeData) VALUES (5, 'lop')
INSERT INTO @MyTable (ROW_NUM, SomeData) VALUES (6, 'cow')
INSERT INTO @MyTable (ROW_NUM, SomeData) VALUES (7, 'moo')


SELECT 'Problem', *
FROM (SELECT *, ROW_NUMBER() OVER (ORDER BY ROW_NUM) rn FROM @MyTable) s
WHERE rn <> ROW_NUM

Answer 2

试试这个：您需要Cast int to varchar 并尝试执行打印的 SQL 以查找错误探测

DECLARE @N          INT = 6, 
        @I          INT = 0, 
        @SQL        NVARCHAR(MAX) 


BEGIN

  SET @SQL = '(CASE WHEN ROW_NUM = '+CAST(@I as VARCHAR(10))+' 
  THEN problem ELSE NULL END) ';
 SET @I = @I+1;
END
print @SQL
EXEC SP_EXECUTESQL @SQL