Ray
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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
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?
Or maybe I just dreamed that?
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.
ASKER
whats the specific syntax because it's not the typical ...
from t1 left join t2 on t2.mycol = t1.mycol
from t1 left join t2 on t2.mycol = t1.mycol
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).
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).
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ASKER
"Using" is what I couldn't remember! Thanks Dave :-)
ASKER
Thanks for the effort Qlemo.
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:
HTH,
DaveSlash
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
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)
HTH,
DaveSlash
ASKER
VERY nice Dave!!! I hope I remember this long enough to use it and turn it into a habit. Thanks for the extra 'tip'!