"Left Join" versus "Outer Join" in MySQL

Posted on 2007-11-16
Last Modified: 2008-02-01
Someone asked me what is the difference between a "Left Join" and an "Outer Join" in MySQL.

My understanding is that they are the same.

Essentially there are three types of join: Left Outer, Right Outer, and Inner. All the others are just names for these.

Is this correct?
Question by:sypder
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Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 20301772
outer join, per se, does not exist. you have to specify LEFT / RIGHT OUTER JOIN.

LEFT JOIN / LEFT OUTER JOIN  are the same.

please see this page for explanations about the different JOIN s:

Author Comment

ID: 20302032
Exactly, this is my understanding.

So what does the question "explain the difference between LEFT JOIN and OUTER JOIN" mean. Since like you said there is no OUTER JOIN and a LEFT JOIN is a LEFT OUTER JOIN.

Unless they meant to write INNER JOIN or it is a trick question.
LVL 143

Accepted Solution

Guy Hengel [angelIII / a3] earned 500 total points
ID: 20302088
if you study the following mysql document, you will see confirmed that the OUTER keyword is optional, and cannot stand alone:

so, either indeed this is a typo, or a trick question...

Author Comment

ID: 20302098
Thanks for confirming that. I did read that document.

It was in a job description I was applying for and it listed that knowing the difference was a key skill. So I figured I should be sure I am right before I head in.


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