SQL Forgein Key Constraints

SQL Foreign Key Constraints

Using Foreign Key Constraints you can maintain some relation between the two table in the database.

A Foreign Key is a column whose value are derived from the primary key or unique key or some other table.

	
create table table_name
(col1 datatype(size) constraints type),
col2 datatype(size),
........
coln datatype(size));

	
create table employee
(eid number(3) unique,
ename varchar2(15),
sal number(5));

Note: If you avoid the unique constraints property then it gives the following error messages "unique constraints scott sys-avoided"