What is foreign key?

Answer 1

In SQL it is a key in a table that points to a primary key in another table. A way to connect tables. You can read more about it here >> http://www.w3schools.com/sql/sql_foreignkey.asp
it can explain it better than I as well 👍

Answer 2

A foreign key is a primary key from one table in another table.

Database containing two tables, Student and Grade. Student contains details about a student (name, age, etc) and Grade contains grade information (when applied, what level, what area).

The student table has a primary key of "STUDENT_ID", so a single STUDENT_ID can identify a single student.
The Grade table has a primary key of "GRADE_ID" so a single grade ID can identify an instance of a grade

To link them together (So we know which student gets which grade), we need a foreign key in the Grade table. Something to tell us which student got that grade. We can add "STUDENT_ID" into the grade table, and then this means we can join the Student table to the Grade table, on the STUDENT_ID.

Now, we can say, which student got which grade.

Does that help?

Answer 3

In the relational databases, a foreign key is a field or a column that is used to establish a link between two tables.

In simple words you can say that, a foreign key in one table used to point primary key in another table.