what is the difference between primary key and foreign key?

   A primary key is a column which uniquely identifies the

records in a table. In a broad sense, a primary key is the

mixture of a unique key and an index: A collumn with a primary

key is indexed to deliver a faster query, and doesn't allow

duplicate values to ensure specific data.

   A foreign key is a column (the child collumn) in a table which

has a corresponding relationship and a dependency on another

collumn (the parent collumn) that is usually in a different

table. Parent collumns can have multiple child collumns, but a

child collumn can only have one parent collumn.