警告：消除空值

Question

我有临时表（见图），列数事故和可预防事故数量应该显示数据，但是它们都显示为全NULL。我如何解决它？谢谢

Answer 1

原因是因为您正在使用空值进行聚合

让我用一个例子解释如下：

create TABLE #test (ID INT, Qty INT, Price MONEY)
INSERT INTO #test (ID, Qty, Price) SELECT 1, 25, 100
INSERT INTO #test (ID, Qty, Price) SELECT 2, NULL, 200
INSERT INTO #test (ID, Qty, Price) SELECT 3, 5, NULL

SELECT SUM(Qty)  FROM #test WHERE ID IN (1,3)
-- no warning
--Because qty in id 1,3 is not null

SELECT SUM(Price) FROM #test WHERE ID IN (1,3)
-- Warning: Null value is eliminated by an aggregate or other SET operation.
-- Because price 100 is added with NULL

SELECT AVG(Qty)  FROM #test WHERE ID IN (1,2)
-- Warning: Null value is eliminated by an aggregate or other SET operation.
-- Because qty is null + 25 to get average