Alternate Keys In SQL Server 2008
In this article we will learn about Alternate Key in SQL Server.
Alternate keys is like primary key that can be a column or group of column of a table whose values are unique at all time. There can be multiple alternate keys in a table and can contain null value unless it is explicitly defined with a NOT NULL integrity rule.
UNIQUE keyword is used to define alternate key. It indicates that value must remail unique.
Create alternate key
create table DepartmentId(
DeptNo integer not null,
Emp_No integer not null unique,
Dep_Name varchar(10) not null,
primary key (DeptNo)
)
Output:
This code can also be written as follows.
create table DepartmentId(
DeptNo integer not null,
Emp_No integer not null,
Dep_Name varchar(10) not null,
primary key (DeptNo),
unique(Emp_No)
)