Hi Luigi,
you will have problems if table 1 and table 2 have the same names to col1 e
col2. For example, table1 has col1=parcel and col2=area and table 2 has
col1=country and col2=area then, in that case you will have ambiguity.
Would you please give me an example?
I have two tables like the following:
T1 (col1 varchar, col2 varchar, primary key (col1, col2))
T2 (col1 varchar, col2 varchar, primary key (col1, col2))
Query I have is:
===================
select col1, col2
from T1
left join T2 using (T1, T2);
Thanks a lot!
2008/8/22 Emi Lu <[EMAIL PROTECTED]>
Hi Edward,
Just a guess, but it seems to me that since the join is using col1 and
col2
there is no ambiguity. They should be the same no matter which table it
comes from.
Not always the same; "Left join" may return:
table2.col1,col2 = null,
while table1.col1,col2 is not null
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:
[EMAIL PROTECTED]
On Behalf Of Emi Lu
Sent: Friday, August 22, 2008 4:12 PM
To: pgsql-sql@postgresql.org
Subject: [SQL] Why *no* ambig.uous complain in select part?
Good morning,
Just notice one small thing, and need your information about select
select col1, col2
from table1
left join table2
using (col1, col2)
;
This query never complain about ambiguous columns of col1 and col2 in the
select part.
My guess is:
(1) col1, col2 always return table1.col1, table1.col2
(2) because using (col1, col2)
that's why, table name is not necessary in select part
Am I wrong? Please advise?
Thank you!
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