I created a postgresql table with a trigger that fills a fields value during insert/update. Postgress has the neat possibility to return that value directly by appending 'RETURNING <fieldname>' to the query. So 
INSERT INTO table (name) VALUES ("Roland684");
SELECT id FROM table WHERE name = "Roland684";

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can be done in one single (and safer) statement like this: 
INSERT INTO table (name) VALUES ("Roland684") RETURNING id;

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Nice!

I've also written a general purpose subroutine that handles SQL-queries, passed to it as a string. And this combination is where some wisdom is required.

How can I check if there are any values returned?

When I execute a query without the RETURNING clause, $sth->fetch will produce the warning message "DBD::Pg::st fetchrow_hashref failed: no statement executing".

While the following code works for both insert/update statements with the returning clause and select statements, even when no records are returned, it fails for insert/update statement without the RETURNING clause. 

my $sth = $dbh->prepare($query);
my $insertedrecords = $sth->execute;
while (my $result = $sth->fetchrow_hashref) {
  ...
}

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(and with 'fails' I mean that it works correctly, but also produces an warning.)

I could check the sql query for the existence of the sub-string " RETURNING ", but we can all imaging when this will fail. Properly parsing the query seems too far fetched, there has to be a simpler way.

In reply to How to detect postgresql RETURNING usage by Roland684

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