Is It Null Or Not Null?

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;