Question

I have the feeling this has a really simple solution and I’m just suffering a brain freeze, but I hope you can help.

I have 2 tables that have identical layouts but data from separate systems and I want to combine them in a query for reporting purposes. But the column I would normally join on may have values that are only in one or the other table.

Table A

Date       | Sales
-------------------
20/12/2010 | 500
19/12/2010 | 450

Table B

Date       | Sales
-------------------
20/12/2010 | 200
18/12/2010 | 70

I want these in a result set as so:

Result

Date       | Sales A | Sales B
-------------------------------
20/12/2010 | 500     |    200
19/12/2010 | 450     |    NULL
18/12/2010 | NULL    |    70

This look so simple and obvious but I can’t get it right, and help would be greatly appreciated.

Answer 1

Using Outer Joins in SQL Server:

Using Full Outer Joins
To retain the nonmatching information by including nonmatching rows in the results of a join, use a full outer join. Microsoft® SQL Server™ 2000 provides the full outer join operator, FULL OUTER JOIN, which includes all rows from both tables, regardless of whether or not the other table has a matching value.

select
  coalesce(TableA.Date, TableB.Date) as Date,
  TableA.Sales as SalesA,
  TableB.Sales as SalesB
from
  TableA
  full join TableB on TableA.Date = TableB.Date