PostgreSQL: how to create a partitioned table using a conversion function

Consider the following table:

CREATE TABLE myuser.mytable (
    id integer NOT NULL,
    created_date timestamp without time zone NOT NULL,
    event_json text NOT NULL,
    format_version text NOT NULL,
    rep_id text NOT NULL,
    appversion text NOT NULL
);

Let's say you want to partition this table by RANGE, and you would like to use the column "created_date" which is of data type "TIMESTAMP WITHOUT TIME ZONE".
You could use a conversion function like CAST to convert the column to a partitioned one, like this:

  CREATE TABLE myuser.mytable (
    id integer NOT NULL,
    created_date timestamp without time zone NOT NULL,
    event_json text NOT NULL,
    format_version text NOT NULL,
    rep_id text NOT NULL,
    appversion text NOT NULL
)
partition by range(cast(created_date as date));

Obviously you proceed with adding your partitions the way you normally would in PostgreSQL, for example:

CREATE TABLE myuser.mytable_p_202001
 PARTITION OF myuser.mytable
 FOR VALUES FROM ('2020.01.01') TO ('2020.01.31');

CREATE TABLE myuser.mytable_p_202002
 PARTITION OF myuser.mytable
 FOR VALUES FROM ('2020.02.01') TO ('2020.02.29');

etc

CREATE TABLE myuser.mytable_p_default
 PARTITION OF myuser.mytable
 DEFAULT;

Beware: If you try to create a primary key constraint on the partition key column in this case, you will receive

DETAIL:  PRIMARY KEY constraints cannot be used when partition keys include expressions.

You are of course free to add a normal search index on the column:

CREATE INDEX myidx1 ON myuser.mytable USING btree ( cast (created_date as date) );

Read more about the CAST function in the documentation
Another good source is postgressqltutorial.com