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OLD sql server sql JOIN syntax

Posted on 2016-08-02
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Last Modified: 2016-08-02
Hi All,
I am having issues converting the old syntax and wondered if any can convert the following to current SQL?

From APOPEN O, APPayments P, APNewPayables N Where O.ApplytoId =* P.ApplytoId  and N.voucherid =* P.applytoid

These are apparently RIGHT OUTER JOINS (i.e. RIGHT JOINS)

I have tried both the following and neither seems to work correctly. I suspect #2 (RIGHT JOIN) is closer than a LEFT join, but maybe the table (JOIN) order needs to be changed?

1. from APOPEN O LEFT JOIN APPayments P ON O.ApplytoId = P.ApplytoId LEFT JOIN APNewPayables N ON N.voucherid = P.applytoid
2. from APOPEN O RIGHT JOIN APPayments P ON O.ApplytoId = P.ApplytoId RIGHT JOIN APNewPayables N ON N.voucherid = P.applytoid

thank you
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Question by:COACHMAN99
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2 Comments
 
LVL 49

Accepted Solution

by:
PortletPaul earned 2000 total points
ID: 41740060
step 1 place each element on a new line

From APOPEN O
, APPayments P
, APNewPayables N
Where O.ApplytoId =* P.ApplytoId  
and N.voucherid =* P.applytoid

step 2 CUT the join condition to align with relevant table

From APOPEN O
, APPayments P O.ApplytoId =* P.ApplytoId  
, APNewPayables N N.voucherid =* P.applytoid
Where
and

step 3 tidy up

From APOPEN O
RIGHT OUTER JOIN APPayments P ON O.ApplytoId =* P.ApplytoId  
RIGHT OUTER JOIN APNewPayables N ON N.voucherid =* P.applytoid

step 4 remove those asterisks

From APOPEN O
RIGHT OUTER JOIN APPayments P ON O.ApplytoId = P.ApplytoId  
RIGHT OUTER JOIN APNewPayables N ON N.voucherid = P.applytoid

===============
personally I prefer
===============
while it makes no difference to the actual execution I prefer to ALWAYS refer to the PRIOR table FIRST

notice the bold here

From APOPEN O
RIGHT OUTER JOIN APPayments P ON O.ApplytoId = P.ApplytoId  

but on the next join

RIGHT OUTER JOIN APPayments P ON O.ApplytoId = P.ApplytoId  
RIGHT OUTER JOIN APNewPayables N ON N.voucherid = P.applytoid

SO, as a final step, get the join conditions consistent

From APOPEN O
RIGHT OUTER JOIN APPayments P ON O.ApplytoId = P.ApplytoId  
RIGHT OUTER JOIN APNewPayables N ON P.applytoid  = N.voucherid

I have previously attempt to explain my approach on "ye olde joins" here:
https://www.experts-exchange.com/articles/13757/Ye-Olde-Joins-how-to-replace-them.html

===========
  and finally
===========

There is an "unwritten convention" amongst many of use who write or maintain mountains of SQL. That convention is: always use left joins (& never use a right join)

Please don't get me wrong, you are completely free to use a right join and the SQL standards allow it. I am simply saying that you can always re-write the right join as a left join. by changing the order of how the tables are called, like this:

From APOPEN O
RIGHT OUTER JOIN APPayments P ON O.ApplytoId = P.ApplytoId  
RIGHT OUTER JOIN APNewPayables N ON P.applytoid  = N.voucherid

becomes

FROM APNewPayables  N
LEFT OUTER JOIN APPayments P  ON N.voucherid = P.applytoid
LEFT OUTER APOPEN O ON P.ApplytoId  = O.ApplytoId
1
 
LVL 7

Author Comment

by:COACHMAN99
ID: 41740070
Hi Paul
thanks for all the info.
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