Re: Using || operator to fold multiple columns into one

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
Kontakt:  Heynitz: 035242/47150,   D1: 0160/7141639 (mehr: -> Header)
GnuPG: 0x31720C99, 1006 CCB4 A326 1D42 6431  2EB0 389D 1DC2 3172 0C99