Question

Given the following data/schema:

DECLARE @t1 TABLE (
    Id int NOT NULL
)

DECLARE @t2 TABLE (
    Id INT NOT NULL,
    Val1 CHAR(1) NOT NULL
)

DECLARE @t3 TABLE (
    Id INT NOT NULL,
    Val2 CHAR(1) NOT NULL
)

INSERT INTO @t1 VALUES (1)
INSERT INTO @t2 VALUES (1, 'A')
INSERT INTO @t2 VALUES (1, 'B')
INSERT INTO @t2 VALUES (1, 'C')
INSERT INTO @t3 VALUES (1, '9')
INSERT INTO @t3 VALUES (1, '8')

I would like to see the following result set:

Id,Val1,Val2
1,'A','9'
1,'B','8'
1,'C',NULL

Now add the following:

INSERT INTO @t3 VALUES (1, '7')
INSERT INTO @t3 VALUES (1, '6')

And I would like to see this:

Id,Val1,Val2
1,'A','9'
1,'B','8'
1,'C','7'
1,NULL,'6'

Here’s what I came up with:

DECLARE @t4 TABLE(
    Id INT NOT NULL,
    RowNumber INT NOT NULL,
    Val1 CHAR(1) NULL,
    Val2 CHAR(1) NULL
)

INSERT INTO @t4 (Id, RowNumber, Val1)
    SELECT Id, ROW_NUMBER() OVER(ORDER BY Id), Val1
        FROM @t2

MERGE @t4 T
USING(SELECT Id, ROW_NUMBER() OVER(ORDER BY Id) RowNumber, Val2 FROM @t3) S
ON (T.Id = S.Id AND T.RowNumber = S.RowNumber)
WHEN MATCHED THEN
    UPDATE SET T.Val2 = S.Val2
WHEN NOT MATCHED THEN
    INSERT (Id, RowNumber, Val2) VALUES (Id, RowNumber, Val2);

SELECT Id, Val1, Val2 FROM @t4

But I’d like to know if someone can come up with something simpler, using SELECT with JOINs instead MERGE

Answer 1

;with q2 as (
    select
        Id,
        Val1,
        ROW_NUMBER() OVER(ORDER BY Val1) rn
    from @t2
), q3 as (
    select
        Id,
        Val2,
        ROW_NUMBER() OVER(ORDER BY Val2 DESC) rn
    from @t3
)
select 
    isnull(q2.Id, q3.Id) as Id, 
    q2.Val1, 
    q3.Val2
from 
    q2 full outer join
    q3 on q2.Id = q3.Id and q2.rn = q3.rn