Re: select t.name from tbl t (where "name" is not a column name)

[Joe Conway <mail@xxxxxxxxxxxxx>]

On 02/23/2010 05:07 PM, raf wrote:
> i've just noticed the following behaviour and was wondering
> if there's any documentation to explain what it's for.
> 
>   create table tbl(id serial primary key, a text, b text, c text);
>   insert into tbl(a, b, c) values ('abc', 'def', 'ghi');
>   insert into tbl(a, b, c) values ('jkl', 'mno', 'pqr');
>   insert into tbl(a, b, c) values ('stu', 'vwx', 'yza');
>   select t.name from tbl t;

I forget exactly where this is documented (and could not find it with a
quick look), but calling t.name is the same as name(t) if a column
reference is not found, and name is a function, which it is.

So t.name is essentially casting the whole row as a name datatype and
outputting the result. Try it with text:

test=# \d foo
      Table "public.foo"
 Column |  Type   | Modifiers
--------+---------+-----------
 f      | integer |

test=# select foo.text from foo;
 text
------
 (-1)
(1 row)

test=# drop TABLE foo;
DROP TABLE

test=# create table foo(f int, text text);
CREATE TABLE

test=# insert into foo values(-1,'abc');
INSERT 0 1

test=# select foo.text from foo;
 text
------
 abc
(1 row)

test=# select foo.name from foo;
   name
----------
 (-1,abc)
(1 row)

HTH,

Joe

Attachment: signature.asc
Description: OpenPGP digital signature