Solved

DB2 Join shortcuts - isn't there a special way you can join if the column name is the SAME in the 2 tables being joined

Posted on 2014-09-24
8
561 Views
Last Modified: 2014-09-25
I seem to recall reading there is a special way you can join if the column name is the SAME in the 2 tables being joined.  The perk to using this method is that when joining on this same column, the result set only gets the column one time.  So if you used this other syntax instead of "from t1 left join t2 on t2.mycol = t1.mycol" then "mycol" would only exist once in the joined result set.

Or maybe I just dreamed that?
0
Comment
Question by:Ray
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
  • 2
  • 2
8 Comments
 
LVL 70

Expert Comment

by:Qlemo
ID: 40342820
That's called a Natural Join, but I can't recall any popular DBMS supporting that. And it is always an Inner Join by definition.
0
 
LVL 11

Author Comment

by:Ray
ID: 40342830
whats the specific syntax because it's not the typical ...
from t1 left join t2 on t2.mycol = t1.mycol
0
 
LVL 70

Expert Comment

by:Qlemo
ID: 40342845
I don't get what you ask for.

Left Join is one kind of Outer Join, allowing one side (the right in this case) to be not matched and still return rows.

The Natural Join has theoretical syntax descriptions, but no implementation in DB2 and many more DBMS. It is "implemented" manually by enumerating the disjunct columns of at least one of the tables, so no change for you. And as said, Natural Join cannot be an Outer Join (left or right or full).
0
Will your db performance match your db growth?

In Percona’s white paper “Performance at Scale: Keeping Your Database on Its Toes,” we take a high-level approach to what you need to think about when planning for database scalability.

 
LVL 18

Accepted Solution

by:
Dave Ford earned 500 total points
ID: 40342886
It works for me on DB2 for i :

select *              
  from deleteme 
  join deleteme2
 using (commonColumn)

Open in new window


HTH,
DaveSlash
0
 
LVL 11

Author Closing Comment

by:Ray
ID: 40343891
"Using" is what I couldn't remember!  Thanks Dave :-)
0
 
LVL 11

Author Comment

by:Ray
ID: 40343893
Thanks for the effort Qlemo.
0
 
LVL 18

Expert Comment

by:Dave Ford
ID: 40344720
I realize this question is already answered, but here's another neat trick for shortening your queries that works beautifully on DB2 for i (v6.1) :

Instead of this:

SELECT someStuff
  FROM Table1 a
  left outer join Table2 b
    on b.column1 = a.column1
   and b.column2 = a.column2
  left outer join Table3 c 
    on c.column1 = b.column1
   and c.column2 = b.column2
   and c.column3 = b.column3
   and c.column4 = b.column4

Open in new window

You can do this:

SELECT someStuff
  FROM Table1 a
  left outer join Table2 b 
    on (b.column1,b.column2) = (a.column1,a.column2)
  left outer join Table3 c
    on  (c.column1,c.column2,c.column3,c.column4) =
        (b.column1,b.column2,b.column3,b.column4)

Open in new window


HTH,
DaveSlash
0
 
LVL 11

Author Comment

by:Ray
ID: 40344965
VERY nice Dave!!!  I hope I remember this long enough to use it and turn it into a habit.  Thanks for the extra 'tip'!
0

Featured Post

Veeam gives away 10 full conference passes

Veeam is a VMworld 2017 US & Europe Platinum Sponsor. Enter the raffle to get the full conference pass. Pass includes the admission to all general and breakout sessions, VMware Hands-On Labs, Solutions Exchange, exclusive giveaways and the great VMworld Customer Appreciation Part

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

When it comes to protecting Oracle Database servers and systems, there are a ton of myths out there. Here are the most common.
Azure Functions is a solution for easily running small pieces of code, or "functions," in the cloud. This article shows how to create one of these functions to write directly to Azure Table Storage.
Video by: Steve
Using examples as well as descriptions, step through each of the common simple join types, explaining differences in syntax, differences in expected outputs and showing how the queries run along with the actual outputs based upon a simple set of dem…
Polish reports in Access so they look terrific. Take yourself to another level. Equations, Back Color, Alternate Back Color. Write easy VBA Code. Tighten space to use less pages. Launch report from a menu, considering criteria only when it is filled…

635 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question