PL/pgSQL: SELECT INTO only if result count = 1

On Sat, 27 Aug 2011 18:45:42 -0300
Osvaldo Kussama <osvaldo.kussama@gmail.com> wrote:

2011/8/27, Tarlika Elisabeth Schmitz
<postgresql6@numerixtechnology.de>:

Hello,

In a PL/pgSQL trigger function, I try to select a record from table
"town" below.

I am only interested in the result if the returned result set
contains exactly one result.
If there is more than one result, I want to log the fact.

EXAMPLE pseudo code

select
country_fk, region_fk, id
from town
where name = 'Newcastle'

if found and count = 1
populate country_id, region_id, town_id
else
raise notice 'ambiguous %', town.name

[...]
--

Use:
GET DIAGNOSTICS integer_var = ROW_COUNT;

SELECT INTO
country_id, region_id, town_id
country_fk, region_fk, id
FROM town
WHERE ...;

GET DIAGNOSTICS cnt = ROW_COUNT;
RAISE DEBUG 'COUNT %', cnt;

always returns 1

--

Best Regards,
Tarlika Elisabeth Schmitz

Tarlika Elisabeth Schmitz <postgresql6@numerixtechnology.de> writes:

SELECT INTO
country_id, region_id, town_id
country_fk, region_fk, id
FROM town
WHERE ...;

GET DIAGNOSTICS cnt = ROW_COUNT;
RAISE DEBUG 'COUNT %', cnt;

always returns 1

Yeah. By default, SELECT INTO just fetches one row and stops;
it doesn't look to see if there are more.

You could possibly use SELECT INTO STRICT and catch the error if
there's more than one row. I suspect though that it'd be more efficient
to use a FOR loop and just note for yourself how many rows you get.

regards, tom lane

On Sat, 27 Aug 2011 18:36:14 -0400
Tom Lane <tgl@sss.pgh.pa.us> wrote:

Tarlika Elisabeth Schmitz <postgresql6@numerixtechnology.de> writes:

SELECT INTO
country_id, region_id, town_id
country_fk, region_fk, id
FROM town
WHERE ...;

GET DIAGNOSTICS cnt = ROW_COUNT;
RAISE DEBUG 'COUNT %', cnt;

always returns 1

Yeah. By default, SELECT INTO just fetches one row and stops;
it doesn't look to see if there are more.

You could possibly use SELECT INTO STRICT and catch the error if
there's more than one row.

What a life saver late on a Saturday night! That does the trick.

--

Best Regards,
Tarlika Elisabeth Schmitz