SQL Server - 从两个表和表中获取数据

Question

请参阅下面的表格和数据 -

DECLARE @test1 TABLE (Ref nvarchar(10) NULL, Dates datetime NULL);
INSERT INTO @test1(Ref, Dates) 
VALUES 
('R1', '2018-10-26'),
('R2', '2018-10-26'),
('R5', null);

DECLARE @test2 TABLE (P_Ref nvarchar(50) null, Name nvarchar(50) null);
INSERT INTO @test2(P_Ref, Name)
VALUES 
('R1', 'N1'),
('R1', 'N2'),
('R2', 'N1'),
('R2', 'N2'),
('R3', 'N1'),
('R3', 'N2'),
('R4', 'N2'),
('R5', 'N3'),
('R6', 'N3'),
('R7', 'N4');

我正在使用表1 @test1 where条件，它的Ref列连接表2 @test2 P_Ref列。 我想要来自两个表的所有相关数据以及@test2表中的所有匹配Name

我的疑问是 -

select t1.Ref, t2.P_Ref, t2.Name from
@test1 t1
right join @test2 t2
on t1.Ref = t2.P_Ref
where t1.Dates is not null

我得到的输出 -

   Ref    P_Ref    Name
    R1      R1      N1
    R1      R1      N2
    R2      R2      N1
    R2      R2      N2

我正在寻找下面的输出 -

   Ref    P_Ref    Name
    R1      R1      N1
    R1      R1      N2
    R2      R2      N1
    R2      R2      N2
    NULL    R3      N1
    NULL    R3      N2
    NULL    R4      N2

有人可以帮助我如何实现这一目标。

提前致谢

Answer 1

请尝试以下查询

SELECT t1.Ref, t2.P_Ref, t2.Name
FROM @test1 t1
RIGHT JOIN @test2 t2 ON t1.Ref = t2.P_Ref
WHERE t2.Name IN(
    SELECT DISTINCT t2.Name
    FROM @test1 t1
    JOIN @test2 t2 ON t1.Ref = t2.P_Ref
    WHERE t1.Dates IS NOT NULL
  )

Answer 2

请尝试以下查询

select t1.Ref, t2.P_Ref, t2.Name from
@test1 t1 right join @test2 t2
on t1.Ref = t2.P_Ref
where Name in ('N1', 'N2')

Answer 3

如果预期有大量记录的Dates可能不是NULL那么优化选项将如下所示。

IF OBJECT_ID('tempdb..#ValidRecords') IS NOT NULL
    DROP TABLE #ValidRecords

SELECT DISTINCT t2.[Name]
INTO #ValidRecords
FROM @test1 t1
JOIN @test2 t2 ON t1.Ref = t2.P_Ref
WHERE t1.Dates IS NOT NULL

SELECT Ref,
t2.P_Ref,
t2.[Name]
FROM @test1 t1
RIGHT JOIN @test2 t2 ON t1.Ref = t2.P_Ref
INNER JOIN #ValidRecords vr ON vr.[Name] = t2.[Name]

Answer 4

问题是您的WHERE子句将外部联接转换为隐式内部联接。 要过滤外部表，通常最简单的方法是将外部表的过滤条件移动到连接条件。

select t1.Ref, t2.P_Ref, t2.Name from
@test1 t1
right join @test2 t2
    on  t1.Ref = t2.P_Ref
    and t1.Dates is not null