Okay just a short explication of the different joins: (What I wrote in parenthesis is just optional):
(Inner) Join: Only rows that are found in both tables/views are returned
Left (Outer) Join: All rows from the first (left) table/view are returned even if there is no match in the second table/view
If there is no equivalent in the second table, NULL values will be returned
Right (Outer) Join: All rows from the second (right) table/view are returned even if there is no match in the first table/view
If there is no equivalent in the second table, NULL values will be returned
Full (Outer) Join: All rows of both tables are returned independent if there is a match or not
(Left) Exception Join: All rows from the first (left) table/view are returned where in the second (right) table/view no match is found
Right Exception Join: All rows from the second (right) table/view are returned where in the first (left) table/view no match is found
Cross Join: All rows of the first table/view are connected to all rows of the second table (cartesian product)
Mit freundlichen Grüßen / Best regards
Birgitta Hauser
Modernization – Education – Consulting on IBM i
"Shoot for the moon, even if you miss, you'll land among the stars." (Les Brown)
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-----Original Message-----
From: MIDRANGE-L <midrange-l-bounces@xxxxxxxxxxxxxxxxxx> On Behalf Of Javier Sanchez
Sent: Freitag, 15. Juli 2022 20:02
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxxxxxxxx>
Subject: Re: Difference between inner join and join in SQL query
Okay, this is it. JOIN and INNER JOIN are just the same. Don't know why the SQL standards took that for granted. LEFT JOIN also would work just fine as well as JOIN as long as you know what you are doing. It's confusing, isn't it. Okay, let's get back. INNER JOIN is the same as JOIN. LEFT JOIN would also be the same thing as JOIN. But putting the OUTER JOIN construct would give you different results depending on what you want to do.
Suppose you have two tables A, and B. Now, if you select ALL records in table A that correspond to the same rows as in table B related with some key columns, that is called a cartesian relationship.
One to one relationship would give you all records in table A that have the same key values as in table B. JOIN or LEFT JOIN or simply JOIN would work well.
Now, here's the difference. Case 1. We want back all rows in table A and also all those in table B that have the same key columns in the ON xxx = yyy part of the SQL statement, but want also to include those rows in table B that DO NOT match the key criteria. Those rows will be returned to you with NULL values. So you'll know they are not in table B.
Case 2. RIGHT OUTER JOIN works in the opposite way. You will get all rows in table B as well as in table A that coincide with the key columns but you'll also get NULL rows in table A that ARE NOT in table B. So you will know what is missing in table A that is not in table B.
Got it?
Javier.
El vie, 15 jul 2022 a las 11:41, jerry ven (<jerryven95@xxxxxxxxx>)
escribió:
Hi,
For the below statement :-
"They simply are not the same and would give different results
depending on what you want back. "
Does it refer with respect to 'INNER JOIN' and 'JOIN' ?
or does it refer to 'LEFT OUTER JOIN' and 'RIGHT OUTER JOIN ' here ?
Could you please clarify ?
Thanks.
On Fri, 15 Jul 2022 at 22:53, Javier Sanchez <
javiersanchezbarquero@xxxxxxxxx> wrote:
LEFT OUTER JOIN and RIGHT OUTER JOIN are a different thing. The
set theory is the base of those constructs. You need to study set
theory.a little more. They simply are not the same and would give
different
results
depending on what you want back.
Javier.
El vie, 15 jul 2022 a las 11:18, Sam_L (<lennon_s_j@xxxxxxxxxxx>)
escribió:
Google 'inner join vs join'
On 7/15/2022 12:58 PM, jerry ven wrote:
Hi,
When I join two files based on ' INNER JOIN' or by simply using
'JOIN'
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