What is the purpose of Unique property in datatable in C#?

Question

Why do we use unique key in data table in C#?

i need answer with syntax.. how to set unique key

objDataColumn.Unique = objDataTable.Columns.Add("Student ID");
objDataTable.Columns.Add("Student Id", typeof(int));

thanks in Advance

Answer 1

Unique constraint will ensure your column will never have duplicate value. see msdn

DataColumn column = new DataColumn("Student ID");
column.DataType = System.Type.GetType("System.Int32");
column.Unique = true;
objDataTable.Columns.Add(column);

Answer 2

Simple:

DataColumn dt = new DataColumn("Student ID", typeof(int));
dt.Unique = true;
objDataTable.Columns.Add(dt);

Or if you're a fan of one-liners:

objDataTable.Columns.Add(new DataColumn("Student ID", typeof(int)) { Unique = true });

Answer 3

for primary key:

DataColumn[] keys = new DataColumn[1];
keys[0] = objDataTable.Columns[0];
objDataTable.PrimaryKey = keys;

for constraint:

var c= new UniqueConstraint(new DataColumn[] { objDataTable.Columns[0]});
objDataTable.Constraints.Add(c);