A primary key is a column or a group of columns that is used to identify a row uniquely in a table.
A table can have only one primary key.
When you add a primary key to a table, PostgreSQL creates a unique index on the column or a group of columns used to define the primary key
Syntax
-- Primary Key
CREATE TABLE table_name (
column_name data_type PRIMARY KEY,
column_name data_type, ...);A foreign key is a field or group of fields in a table that unique identifies a row in another table.
In other words, a foreign key is defined in a table that refers to the primary key of the other table.
The table that contains the foreign key is called referencing table or child table. And the table to which the foreign key references is called referenced table or parent table
A table can have multiple foreign keys depending on its relationships with other tables.
Define foreign keys through a foreign key constraint