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SQL COUNT() Function

SQL FOREIGN KEY Constraint

A FOREIGN KEY in one table focuses to a PRIMARY KEY in another table.

Let's show the outside key with a precedent. Take a gander at the accompanying two tables:

The "Persons" table:

User_Id UserName UserName Password Email
1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger

The "Orders" table:

O_Id OrderNo User_Id
1 501 3
2 502 3
3 503 2
4 504 1