RE: Using a different column name in a foreign table

Thanks Adrian. I was aware of that.

But...in the case of FT definition, the quotes are mandatory after column_name in options. And it is a single quote.
The problem here may be is that the "create foreign table" statement accepts only lower case  after options. Remember
thatthe double quotes for the column name in the "select" statement is generated by postgres, not by the end user. If
thedouble quotes were not present, the query with the upper case would have worked.
 

A.A.

-----Original Message-----
From: Adrian Klaver [mailto:adrian.klaver@aklaver.com]
Sent: Friday, January 21, 2022 1:14 PM
To: Alanoly Andrews <alanolya@invera.com>; Tom Lane <tgl@sss.pgh.pa.us>; Guillaume Lelarge <guillaume@lelarge.info>
Cc: pgsql-general@lists.postgresql.org
Subject: Re: Using a different column name in a foreign table

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On 1/21/22 10:04 AM, Alanoly Andrews wrote:
> Following up on my previous message, there was a related problem with
> FT definitions for which I have a workaround. It seems that the new
> column_name after "options" in an FT definition cannot be in upper case.
> See below:
> When I define a foreign table like below, I get an error in the
> subsequent select statement:
> create foreign table scvmgl_rec (
> MGL_CLNT_HOST_NM char(15) options (column_name 'MSG_CLNT_HOST_NM'))
> server pglpolaris12018 options (schema_name 'informix', table_name
> 'sctmsg_rec'); ai01pr00=# select * from scvmgl_rec;
> ERROR:  column "MSG_CLNT_HOST_NM" does not exist
> CONTEXT:  Remote SQL command: SELECT "MSG_CLNT_HOST_NM" FROM
> informix.sctmsg_rec But when I define the FT as below, there is no
> error in the subsequent "select".
> create foreign table scvmgl_rec (
> mgl_clnt_host_nm char(15) options (column_name 'msg_clnt_host_nm'))
> server pglpolaris12018 options (schema_name 'informix', table_name
> 'sctmsg_rec'); So, apparently postgres transmits the remote query with
> double quotes around the upper-case column name; and such a query
> comes back with "column does not exist". But a double quote around a
> lower-case column name does not produce the error.
> Is this a bug that needs to be fixed? I always thought that table
> names and column names were case-insensitive with regard to SQL's.

You thought wrong:

https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS

'Quoting an identifier also makes it case-sensitive, whereas unquoted names are always folded to lower case. For
example,the identifiers FOO, foo, and "foo" are considered the same by PostgreSQL, but "Foo" and "FOO" are different
fromthese three and each other. (The folding of unquoted names to lower case in PostgreSQL is incompatible with the SQL
standard,which says that unquoted names should be folded to upper case.
 
Thus, foo should be equivalent to "FOO" not "foo" according to the standard. If you want to write portable applications
youare advised to always quote a particular name or never quote it.)'
 

> A.A.
>
--
Adrian Klaver
adrian.klaver@aklaver.com

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