Just for the record, here's the same thing for SQLite. As above, the TRIGGER Dummy_Test_dupe is optional and I haven't tested the performance difference yet.

use warnings;
use strict;
use DBI;

my $dbh = DBI->connect("dbi:SQLite:dbname=:memory:", undef, undef,
    { RaiseError=>1, AutoCommit=>1 } );

$dbh->do(<<'ENDSQL');
CREATE TABLE Dummy_Test (
    Timestamp INTEGER PRIMARY KEY,
    Foo TEXT,
    Bar TEXT
);
ENDSQL
$dbh->do(<<'ENDSQL');
CREATE TRIGGER Dummy_Test_dupe BEFORE UPDATE ON Dummy_Test FOR EACH RO
+W
    WHEN ( OLD.Timestamp IS NEW.Timestamp AND OLD.Foo IS NEW.Foo AND O
+LD.Bar IS NEW.Bar )
    BEGIN SELECT RAISE(IGNORE); END;
ENDSQL
$dbh->do(<<'ENDSQL');
CREATE TRIGGER Dummy_Test_modify BEFORE UPDATE ON Dummy_Test FOR EACH 
+ROW
    WHEN ( OLD.Foo IS NOT NEW.Foo OR OLD.Bar IS NOT NEW.Bar )
    BEGIN SELECT RAISE(ABORT, "same Timestamp but different values"); 
+END;
ENDSQL

my $in = $dbh->prepare(<<'ENDSQL');
INSERT INTO Dummy_Test (Timestamp,Foo,Bar) VALUES (?,?,?)
    ON CONFLICT (Timestamp) DO UPDATE SET Foo=EXCLUDED.Foo, Bar=EXCLUD
+ED.Bar;
ENDSQL

$in->execute(12345,'Hello','World');
$in->execute(12345,'Hello','World');
my $e;
eval { $in->execute(12345,'Hello','abcde'); 1 } or do { $e = $@ };
if ( defined $e ) { print "Third insert failed as expected: $e" }
else { die "Third insert didn't fail as expected" }
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