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Re: using ordinal_position

From: Igor Neyman <ineyman(at)perceptron(dot)com>
To: "johnf(at)jfcomputer(dot)com" <johnf(at)jfcomputer(dot)com>, "pgsql-sql(at)postgresql(dot)org"<pgsql-sql(at)postgresql(dot)org>
Subject: Re: using ordinal_position
Date: 2012-06-11 13:53:54
Message-ID: A76B25F2823E954C9E45E32FA49D70EC08E406A7@mail.corp.perceptron.com (view raw or flat)
Thread:
Lists: pgsql-sql

> -----Original Message-----
> From: John Fabiani [mailto:johnf(at)jfcomputer(dot)com]
> Sent: Thursday, June 07, 2012 7:18 PM
> To: pgsql-sql(at)postgresql(dot)org
> Subject: using ordinal_position
> 
> I'm attempting to retrieve data using a select statement without
> knowing the column names. I know the ordinal position but not the name
> of the column (happens to be a date::text and I have 13 fields).
> 
> Below provides the name of the column in position 3:
> 
> select column_name from (select column_name::text, ordinal_position
> from information_schema.columns where
> table_name='wk_test') as foo where ordinal_position = 3;
> 
> But how can I use the above as a column name in a normal select
> statement.
> 
> Unlike other databases I just can't use ordinal position in the select
> statement - RIGHT???
> 
> Johnf

David gave you already pretty complete answer.
I just wonder what are these "other" RDBMSs that allow to use ordinal column positions in a query?
I am familiar with a few (in addition to Postgress), and none of them does that, not in "select" list., though everybody allow ordinal position from "select" list in "order by" and "group by".

Regards,
Igor Neyman



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