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SQL Server SQL syntax =* and right joins

Hi Folks.
I am struggling to understand the join conversion process, and how to nest right joins.

do the following have identical results?

thank you.

from APOPEN O,APPayments P, APNewPayables N  WHERE O.ApplytoId =* P.ApplytoId and N.voucherid =* P.applytoid

from (APOPEN RIGHT JOIN APPayments ON AOPEN.ApplytoId = APPayment.ApplytoId) RIGHT JOIN APNewPayables ON APNewPayables.voucherid = APPayment.applytoid
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COACHMAN99
Asked:
COACHMAN99
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1 Solution
 
Chris LuttrellSenior Database ArchitectCommented:
Close, SQL Server uses the ANSI JOIN syntax like you have in the second line. The =* is signifying RIGHT OUTER JOIN.  You don't have to have the Parenthesis either.
from APOPEN O RIGHT OUTER JOIN APPayments P ON O.ApplytoId = P.ApplytoId RIGHT OUTER JOIN APNewPayables N ON  N.voucherid = P.applytoid 

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COACHMAN99Author Commented:
Hi Chris
your text is jumping around so I cant read it.
Is right outer not the same as right? and
Do my two statements generate identical results?
thanks
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COACHMAN99Author Commented:
and can one not just use the table-name instead of the alias?
My objective is to use the second text/syntax in place of the first. I just need to know if the results (as I have phrased them) would be identical .

thanks
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Chris LuttrellSenior Database ArchitectCommented:
Yes to both of you questions.  https://msdn.microsoft.com/en-us/library/ms177634(v=sql.130).aspx is the link to the T-SQL rules on FROM.
So OUTER is "OPTIONAL" but I am a fan of following the standards because it will transfer between databases better and you don't have to worry about old code breaking because they suddenly start enforcing the ANSI standards.  I also like table aliases over full table names, just a preference there.
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Chris LuttrellSenior Database ArchitectCommented:
I should know about old code because I have been working with various database versions and vendors for 30 years now and have plenty of my own out there. :-)
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COACHMAN99Author Commented:
Excellent thanks! so my syntax is identical? I was concerned that the second RIGHT join was the wrong way around.
cheers.
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PortletPaulCommented:
There is an unwritten convention: avoid right joins

Please don't get me wrong here. You are free to use any join you want at any time and the standards do allow you to do it. But many of us who write and maintain mountains of SQL prefer to avoid right joins completely making query logic much simpler to maintain.

Your query could be reversed in direction
FROM APNewPayables N
LEFT JOIN APPayments P ON  N.voucherid = P.applytoid 
LEFT JOIN APOPEN O ON P.ApplytoId = O.ApplytoId 

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COACHMAN99Author Commented:
Thanks Paul, makes sense.
So there are no efficiency issues, just 'trickier' to understand?
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Chris LuttrellSenior Database ArchitectCommented:
Good point Paul.  I agree, I just did not want to push the issue.  Yes, they work the same, just trickier to think about the logic flow.
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COACHMAN99Author Commented:
Great to have consensus  :-)
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PortletPaulCommented:
Right joins are indeed much trickier to follow, and they alter the precedence of tables, and in large multi-table from clauses it can be very hard to understand the author's intentions if precedence flips about like a trout on a river bank.

There should not be performance issues as it is actually the optimizer that determines the actual execution path.
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