Outer Joins : which side does the (+) go on

March 5th, 2014

Bobby Durrett just put together a great little post on “outer joins : where do I put the (+)“.

I also have hard time remembering, and below is my cheat sheet using graphics.

If English and French both have a unique key on the “ordinal_id” then it’s basically one-to-one relationship

We add an arrow in the middle of the line to denote “outer join”. The arrow points from the table that drives the join, ie all the rows in the table pointed from are returned even if a match isn’t found in the table pointed to.

            

above graphic originally on http://blog.mclaughlinsoftware.com/oracle-sql-programming/basic-sql-join-semantics/

type ANSI ANSI 89 (Oracle) type type
inner join english INNER JOIN french
using (ordinal_id)
english e, french f 
where e.ordinal_id=f.ordinal_id
left outer join english LEFT JOIN french
using (ordinal_id)
english e, french f 
where e.ordinal_id=f.ordinal_id(+)
right outer join english RIGHT JOIN french
using (ordinal_id)
english e, french f 
where e.ordinal_id(+)=f.ordinal_id
full join english FULL JOIN french
using (ordinal_id)
english e, french f
where e.ordinal_id=f.ordinal_id(+)
UNION
english e, french f
where e.ordinal_id(+)=f.ordinal_id
     


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