Question

所以我必须编写一个查询，显示城市，平均要价和房产数量，以及超过100个房产的城市的总数。我有代码：

SELECT Property.City, '$' + CONVERT(NVARCHAR, AVG(Listing.AskingPrice),1) AS 'Avg. Asking Price', COUNT(Property.PropertyID) AS 'No. of Properties'
FROM Property 
INNER JOIN Listing
ON Property.PropertyID = Listing.PropertyID
GROUP BY Property.City
HAVING COUNT(Property.PropertyID) > 100

但是，结果应该有3行Arcata，Eureka和NULL。我只是让前两个出现..我如何制作它以便我的代码也计算空值？

Answer 1

INNER JOIN忽略匹配的NULL值。只需尝试以下示例进行验证：

DECLARE @T1 TABLE
(
    a int,
    b int
)

DECLARE @T2 TABLE
(
    a int,
    b int
)

INSERT INTO @T1 (a,b)
VALUES(1,2)

INSERT INTO @T1 (a,b)
VALUES(NULL,3)

INSERT INTO @T2 (a,b)
VALUES(1,2)

INSERT INTO @T2 (a,b)
VALUES(NULL,3)

SELECT *
FROM @T1 AS T1
INNER JOIN @T2 AS T2 ON T1.a = T2.a

如果要将结果集设为NULL，请改用LEFT JOIN

DECLARE @T1 TABLE
(
    a int,
    b int
)

DECLARE @T2 TABLE
(
    a int,
    b int
)

INSERT INTO @T1 (a,b)
VALUES(1,2)

INSERT INTO @T1 (a,b)
VALUES(NULL,3)

INSERT INTO @T2 (a,b)
VALUES(1,2)

INSERT INTO @T2 (a,b)
VALUES(NULL,3)

SELECT *
FROM @T1 AS T1
LEFT JOIN @T2 AS T2 ON T1.a = T2.a

如何获取空值显示？

1 个答案: