Relational databases map relationships
Between tables:
A driver has many vehicles.
Between rows across tables:
Driver Amy has 2 vehicles: a 2018 Nissan and a 2017 Ninja.
A foreign key is stored on what is known as the child table, which retrieves the primary key in the parent table, mapping a relationship from parent to child.
The foreign key is always stored in the child table and we say that a child object belongs to a parent objects through the foreign key that’s stored on the child table.
SELECT make, model, year FROM vehicles
JOIN drivers
ON vehicles.driver_id = drivers.id
WHERE drivers.name = 'Sarah';
Parent table: drivers
Child table: vehicles
Primary key (on parent): drivers.id
Foreign key (on child): vehicles.driver_id
An INNER join selects all rows from both tables that have a match between the columns.
By default, in SQL, specifying the keyword JOIN (with no prefix) refers to a/an INNER JOIN.