https://selectstarsql.com/ may help you for JOIN I recommend that your do it in its entirety even if you understand the first concepts

`join` isn't so bad -- you are connecting two tables based on a common value.

If you have `person` and `address`:

    create table person (
        id serial primary key,
        first_name text not null,
        last_name text not null,
        date_of_birth date not null
    );

    create table address (
        id serial primary key,
        person_id integer not null references person (id),
        street_number text not null,
        apartment_number text,
        city text not null,
        state text,
        postal_code text not null
    );

Then you'd join using `person.id` to `address.person_id`. An inner join hides rows from the joining table if there is no corresponding row in the joined-to table, while an outer join includes rows from the joining table if there are no corresponding rows in the joined-to table.

If we've got:

    insert into person (first_name, last_name, date_of_birth)
    values ('Brian', 'Kernighan', '1950-01-01'),  -- gets id 1
           ('Dennis', 'Ritchie', '1948-01-01');   -- gets id 2

    insert into address (person_id, street_number, city, postal_code)
    values (1, '123 Main St.', 'Berkeley', '94701');

Then these two queries will return one and two rows, respectively:

    -- an inner join, only returns `person` rows with a corresponding
    -- row in the `address` table
    select person.first_name,
           person.last_name,
           address.street_number,
           address.city,
           address.postal_code
    from person
      inner join address on person.id = address.person_id
    -- output:
    --  first_name | last_name | street_number |   city   | postal_code
    --  Brian      | Kernighan | 123 Main St.  | Berkeley | 94701



    -- a left outer join, returns all `person` rows, regardless of
    -- the existence of a corresponding row in the `address` table
    select person.first_name,
           person.last_name,
           address.street_number,
           address.city,
           address.postal_code
    from person
      left outer join address on person.id = address.person_id

    -- output:
    --  first_name | last_name | street_number |   city   | postal_code
    --  Brian      | Kernighan | 123 Main St.  | Berkeley | 94701
    --  Dennis     | Ritchie   |               |          |

One important thing to know is if you are joining to multiple tables, and there are multiple corresponding rows (i.e., a `favorite_food` table with three rows per person, and a `favorite_color` table with three rows per person), you will get _multiplicative_ data -- `n_favorite_foods * n_favorite_colors` rows will be returned per person! This is where things like `group by` and `distinct` come into play.

There are other types of joins, but these two are the usual suspects in most queries.