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Return non-matching rows from both tables

Rudy Limeback EXPERT RESPONSE FROM: Rudy Limeback

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QUESTION POSED ON: 25 January 2008
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?


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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.



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