CTE containing ambiguous columns
Suppose you do this:
create table animals (id serial primary key, name varchar not null);
Then you can do this:
with beings as (select * from animals) select * from beings where id = 1;
But not this:
with beings as (select * from animals a1, animals a2) select * from
beings where id = 1;
Because:
ERROR: column reference "id" is ambiguous at character 82
STATEMENT: with beings as (select * from animals a1, animals a2)
select * from beings where id = 1;
ERROR: column reference "id" is ambiguous
LINE 1: ...m animals a1, animals a2) select * from beings where id = 1;
^
My email program will probably mangle this, so the error cursor here
is point to "id = 1", at the end, and saying that's ambiguous. Which
is sorta kinda true, but the usual remedy of qualifying it with a
relation name (here, beings.id) fails. And you can't quantify it with
a1.id or a2.id either, they're out of scope. In some sense, the real
problem is with "select *", because that is what is expanding into a
non-unique list of column names. But you don't actually trigger an
error unless you try to reference one; the same query works fine
without the where clause.
I'm not sure if there's anything useful we can do about this, but it
definitely threw me for a loop.
...Robert
Robert Haas <robertmhaas@gmail.com> writes:
Suppose you do this:
create table animals (id serial primary key, name varchar not null);
Then you can do this:
with beings as (select * from animals) select * from beings where id = 1;
But not this:
with beings as (select * from animals a1, animals a2) select * from
beings where id = 1;
No different from
regression=# select * from (animals a1 cross join animals a2) x where id = 1;
ERROR: column reference "id" is ambiguous
LINE 1: ...ct * from (animals a1 cross join animals a2) x where id = 1;
^
There's no way to access the a1/a2 aliases here, either; and that rule
goes back to SQL92 or maybe further.
regards, tom lane
Robert Haas wrote:
create table animals (id serial primary key, name varchar not null);
...
with beings as (select * from animals a1, animals a2) select * from
beings where id = 1;
"Doctor, it hurts when I do this."
"So stop doing that."
Can't you disambiguate it using a column list on beings?
cheers
andrew
On Fri, Nov 13, 2009 at 8:32 AM, Andrew Dunstan <andrew@dunslane.net> wrote:
Robert Haas wrote:
create table animals (id serial primary key, name varchar not null);
...
with beings as (select * from animals a1, animals a2) select * from
beings where id = 1;"Doctor, it hurts when I do this."
"So stop doing that."Can't you disambiguate it using a column list on beings?
Sure, after I figured out what the real problem was. Maybe I'm a
dope, but when I get an error cursor pointed at an ambiguous column
reference, my thought is "oh, I need to qualify that reference" - not
"oh, some completely unrelated part of the query has an *-expansion
that contains duplicate columns". Something like:
HINT: <alias> contains multiple columns named <colname>
...would help a lot. I don't feel strongly about it, I just thought
it was confusing.
...Robert
Can't you disambiguate it using a column list on beings?
Sure, after I figured out what the real problem was. Maybe I'm a
dope, but when I get an error cursor pointed at an ambiguous column
reference, my thought is "oh, I need to qualify that reference" - not
"oh, some completely unrelated part of the query has an *-expansion
that contains duplicate columns". Something like:HINT: <alias> contains multiple columns named <colname>
...would help a lot. I don't feel strongly about it, I just thought
it was confusing....Robert
+1
This error would be clearer with something as simple as putting the ^ in the
right place and extremely clear with the above "HINT".
--
--Dan