PostgreSQL: handle query that returns no data

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: remove prepare method

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: implement query sibling methods

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: add fields to query

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: fix typo

Signed-off-by: swpd <swpdtz@gmail.com>