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
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