Re: Ugly problem with USING vs ON in JOIN

Joe,

The problem is that while IBM added USING at v5r4, they didn't
implement it correctly.

It got fixed at 6.1, but not PTF'ed back to v5r4.

This works at v5r4 but not 6.1:
select a.key, b.key, a.data, b.data
from fileA A join fileb B using (key)

this works at 6.1 but not 5.4
select key, a.data, b.data
from fileA A join fileb B using (key)

The fix is good because at 6.1 you can do this:
select key, a.data, b.data, c.data
from fileA A
join fileb B using (key)
join filec C using (key)

There should be some posts from me from a while ago discussing the
issue. My decisions was to only use JOIN USING at v5r4 in ad-hoc
stuff. Production SQL had to continue to use the JOIN ON syntax.

Charles


On Mon, Mar 14, 2011 at 11:27 AM, Joe Pluta <joepluta@xxxxxxxxxxxxxxxxx> wrote:

Here's a real beauty.  Try this with any file:

with t1 as (select key1, data1 from myfile)
  select t1.* from t1 join myfile using (key1)

Then try this:

with t1 as (select key1, data1 from myfile)
  select t1.* from t1 join myfile on t1.key1 = myfile.key1


myfile is any file with a single unique key field.  key1 is that key
field.  data1 is any other field in the file.  Actually, it doesn't HAVE
to be that way; you can use any two fields.  But if you don't use a
unique field you may end up with a REALLY big result set.

The first select will return only data1 in the result set, while the
second will return both key1 and data1.  I'm one behind on DB2 group
PTFs, but this is a pretty big one and it just bit me badly.

Please note that this is a completely stripped down query and I realize
that it effectively does "select key1, data1 from myfile".  The actual
query is much more involved.  But this reproduces the problem in the
fewest steps.

Now I have to start looking for USING in all my queries.

Joe


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