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Return non-matching rows from both tables
An Oracle user asks how to return only non-matching rows when joining two tables.
Is there a way of joining two tables to return only non-matching rows? For example, Table1 and Table2 have an identical structure and contain only two columns:
Table1 ID Name 1 John 2 Philip Table2 ID Name 1 John 3 Andy
The query should return only the following rows:
ID Name 2 Philip 3 Andy
Currently I am using Unions and NOT IN clause. Is there another way?
Try a FULL OUTER JOIN with IS NULL tests:
select coalesce(Table1.ID,Table2.ID) as ID
, coalesce(Table1.Name,Table2.Name) as Name
from Table1
full outer
join Table2
on Table2.ID = Table1.ID
where Table1.ID is null
or Table2.ID is null
Neat, eh?
The only difficulty you might have is that not every database management system supports FULL OUTER JOIN. Many do, because it is part of the SQL standard. If yours doesn't, the UNION is your fallback strategy. My preference is LEFT OUTER JOIN with an IS NULL test as opposed to a NOT EXISTS subquery.
This was last published in January 2008
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