Constaints

Constrain is nothing but it is an condition, it is might be any type of condition. and second one is unique and not null means unique is maintain one record do not accept duplicate record . not null means it is an datatype constraint in the particular column does not accept any null values should be need a value in that field.

Constraints are used for filter the data as transformer stage and from in sql different type of constrains having null, isnull, primarykey,foreign key and unique constrains Ans unique constrain is not allowed duplicate values and Notnull constrain means should be having a data in that column.