sub insert_unique( $table, $column, $value ) {
    state %sths;
    if ( !exists $sths{$table} ) {
        $sths{$table}{SELECT} =
            $dbh->prepare("SELECT id FROM $table WHERE $column = (?)");
        $sths{$table}{INSERT} =
            $dbh->prepare("INSERT INTO $table ($column) VALUES (?) RETURNING id");
    }
    my $rowid;
    my $sth = $sths{$table}{SELECT};
    $sth->execute($value);
    my $rows = $sth->fetchall_arrayref( {} );
    if ($rows->@*) {
        $rowid = $rows->[0]->{id};
    }
    else {
        $sth = $sths{$table}{INSERT};
        $sth->execute($value);
        $rows = $sth->fetchall_arrayref( {} );
        $rowid = $rows->[0]->{id};
    }
    return $rowid;
}