SQL Server全部外部联接返回具有所有NULL值的行

Question

When joining two tables using Full Outer Join, I am receiving results with NULL values in every column. The row count is the same as the count of the larger table. I would expect that at least one table columns would have values. Here is my simple select statement:

SELECT * FROM InputXML X 
FULL OUTER JOIN ACM ON X.[file_name] = ACM.AllCharts

Answer 1

这是一个完全连接，它将在左侧或右侧返回null，但是如果返回的行中包含null，则必须检查是否具有X. [file_name]或ACM.AllCharts带有Null值，因为当您比较null时= null不会给您任何结果，因为null不是一个值，它在数学上有点未知或无限。