In PostgreSQL, the standard way to check if something is NULL
is like so:
select * as wild_pokemons from pokemons where trainer_id is null;
To check if something is not null, you just add not
:
select * as captured_pokemons from pokemons where trainer_id is not null;
PostgreSQL also comes with ISNULL
and NOTNULL
which are non-standard
ways of doing the same as above:
select * as wild_pokemons from pokemons where trainer_id isnull;
select * as captured_pokemons from pokemons where trainer_id notnull;