Date: Wed, 23 Dec 2009 09:50:31 +0100
From: "A. Kretschmer" <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: Using || operator to fold multiple columns into one
Message-ID: <20091223085031.GA12007@a-kretschmer.de>
References: <4B31D619.1090706@obviously.com>
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In response to Bryce Nesbitt :
> Dear experts,
> 
> This point is confusing me with the || operator. I've got a table with
> "one column per data type", like so:
> 
> # \d context_keyvals;
>             Table "public.context_keyvals"
>    Column    |            Type             | Modifiers
> -------------+-----------------------------+-----------
>  context_key | integer                     | not null
>  keyname     | text                        |
>  t_number    | integer                     |
>  t_string    | text                        |
>  t_boolean   | boolean                     |
>  t_date      | timestamp without time zone |
> Indexes:
>     "context_keyvals_ck" btree (context_key) CLUSTER
> Foreign-key constraints:
>     "context_keyvals_context_key_fkey" FOREIGN KEY (context_key)
> REFERENCES contexts(context_key) ON DELETE CASCADE
> # select version()
> PostgreSQL 8.3.8 on x86_64-pc-linux-gnu, compiled by GCC gcc-4.3.real
> (Debian 4.3.2-1.1) 4.3.2
> 
> ------------------------------
> Just for pretty sake I'd like to be able to use psql to view it like this:
> 
> # select context_key,keyname,t_number||t_string||t_date||t_boolean as
> value from context_keyvals;
> 
> But it is not working, the columns always come up empty.  I can use the
> || operator to concatenate strings:
> # select '--'||t_number::text from context_keyvals;
> 
> But the moment I try to combine columns, the result is blank.
> # select '--'||t_number::text||t_string::text from context_keyvals;

At least one column contains NULL. To handle that, use
coalesce(column,'') to change NULL to ''.


Andreas
-- 
Andreas Kretschmer
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