Question

I’ve scoured StackOverflow and Google for an answer to this problem.

I’m trying to create a Microsot SQL Server 2008 view. Not a stored procedure. Not a function. Just a query (i.e. a view).

I have three tables. The first table defines a common key, let’s say “CompanyID”. The other two tables have a sometimes-common field, let’s say “EmployeeName”.

I want a single table result that, when my WHERE clause says “WHERE CompanyID = 12” looks like this:

CompanyID | TableA    | TableB
12        | John Doe  | John Doe
12        | Betty Sue | NULL
12        | NULL      | Billy Bob

I’ve tried a FULL OUTER JOIN that looks like this:

SELECT Company.CompanyID,
    TableA.EmployeeName,
    TableB.EmployeeName
FROM Company
FULL OUTER JOIN TableA ON Company.CompanyID = TableA.CompanyID
FULL OUTER JOIN TableB ON 
    Company.CompanyID = TableB.CompanyID AND 
    (TableA.EmployeeName IS NULL OR TableB.EmployeeName IS NULL OR TableB.EmployeeName = TableA.EmployeeName)

I’m only getting the NULL from one matched table, I’m not getting the expansion for the other table. In the above sample, I’m basically only getting the first and third rows and not the second.

Can someone help me create this query and show me how this is done correctly?

BTW I already have a stored procedure that looks very clean and populates an in-memory table, but that isn’t what I want.

Thanks.

— EDIT:

Here’s a full-running sample of what currently doesn’t work (it’s missing ‘someone 2’ and ‘someone 3’.

DECLARE @Company TABLE
(
    CompanyID int
)

INSERT INTO @Company (CompanyID) VALUES (10)
INSERT INTO @Company (CompanyID) VALUES (12)

DECLARE @TableA TABLE
(
    EmployeeId int,
    CompanyId int,
    EmployeeName varchar(30)
)

DECLARE @TableB TABLE
(
    EmployeeId int,
    CompanyId int,
    EmployeeName varchar(30)
)

INSERT INTO @TableA ( EmployeeId, CompanyId, EmployeeName )
VALUES ( 1, 10, 'someone' )

--INSERT INTO @TableA ( EmployeeId, CompanyId, EmployeeName )
--VALUES ( 2, 12, 'someone 2' )

INSERT INTO @TableA ( EmployeeId, CompanyId, EmployeeName )
VALUES ( 3, 12, 'someone 3' )

INSERT INTO @TableA ( EmployeeId, CompanyId, EmployeeName )
VALUES ( 3, 12, 'someone 4' )

INSERT INTO @TableB ( EmployeeId, CompanyId, EmployeeName )
VALUES ( 1, 10, 'someone' )

INSERT INTO @TableB ( EmployeeId, CompanyId, EmployeeName )
VALUES ( 2, 12, 'someone 2' )

--INSERT INTO @TableB ( EmployeeId, CompanyId, EmployeeName )
--VALUES ( 3, 12, 'someone 3' )

INSERT INTO @TableB ( EmployeeId, CompanyId, EmployeeName )
VALUES ( 3, 12, 'someone 4' )

SELECT Company.CompanyID,
    TableA.EmployeeName,
    TableB.EmployeeName
FROM @Company Company
FULL OUTER JOIN @TableA TableA ON Company.CompanyID = TableA.CompanyID
FULL OUTER JOIN @TableB TableB ON Company.CompanyID = TableB.CompanyID
WHERE
(
    TableA.EmployeeName IS NULL OR TableB.EmployeeName IS NULL OR 
    TableB.EmployeeName = TableA.EmployeeName
)
AND Company.CompanyID = 12

Result:

CompanyID   EmployeeName    EmployeeName
12          someone 4       someone 4

What I want:

CompanyID   EmployeeName    EmployeeName
12          NULL            someone 2
12          someone 3       NULL
12          someone 4       someone 4

Answer 1

The FULL OUTER JOIN should be made only between TableA and TableB on companyID AND employeeName since this is the value you want filled as NULL if it exists only on one table.
Once you get this, you can do an inner join with Company to get other data from Company.

FULL OUTER JOIN Solution:

select Company.companyID, EmployeeNameA, EmployeeNameB
from (
    SELECT isnull(TableA.CompanyID, TableB.CompanyID) as companyID,
        TableA.EmployeeName as EmployeeNameA,
        TableB.EmployeeName as EmployeeNameB
    FROM @TableA TableA 
    FULL OUTER JOIN @TableB TableB ON TableA.EmployeeName = TableB.EmployeeName and TableA.companyID = TableB.companyID
    WHERE
     TableA.CompanyID = 12 or TableB.CompanyID = 12 
) merged
inner join @Company Company
    on merged.companyID = Company.companyID

Personally I find it difficult to think in terms of FULL OUTER JOINS. My approach on this would be: Find the distinct EmployeeNames you need in your result by making a UNION between affected tables and then use left joins to get data from both tables thus getting your NULLs when you should.

LEFT JOIN Example:

select c.companyID, a.employeeName, b.employeeName
from  (
    select distinct employeeName, companyID
    from  (
        select a.employeeName, companyID 
        from @tableA  a
        union 
        select b.employeeName, companyID
        from @tableB b
    ) a
) z
inner join @company c
    on c.companyID = z.companyID
left join @tableA  a
    on z.companyID = a.companyID and z.employeeName = a.employeeName
left join @tableB  b
    on z.companyID = b.companyID and z.employeeName = b.employeeName
where z.companyID = 12