当我在撇号之前删除一些空格时，为什么字符串连接失败？

Question

这有效：

DECLARE @query as nvarchar(200);
SET @query = 'SELECT j.job FROM ' + '' + 'job as j';

EXEC sp_executesql @query

...但这不起作用（输出错误为Incorrect syntax near the keyword 'as', pointing to the first line）：

DECLARE @query as nvarchar(200);
SET @query = 'SELECT j.job FROM' + '' + 'job as j'; -- removed the white space after the word FROM

EXEC sp_executesql @query

为什么会这样？

Answer 1

因为在from之前job之后需要一个空格。

select 'SELECT j.job FROM ' + '' + 'job as j';

返回：SELECT j.job FROM job as j

select 'SELECT j.job FROM' + '' + 'job as j';

返回：SELECT j.job FROMjob as j