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SQLSERVER_6: Constrains in SQL Server

Constraints or validations are a well known phenomenon in and Database Management system to ensure that the columns can receive values that are well within the limit and restrictions imposed. For e.g. we can impose a check on a column named “Age” that the value should be between 20 – 40 only. This can be achieved by the following constraint

Create Table EmpTemp
(
Age numeric(10) constraint age_check check (age between 20 and 40)
)

There are different kinds of constraints in SQL Server:

A  PRIMARY KEY CONSTRAINT

This constraint is to ensure that we can differentiate between two rows in a table. There can only be one primary key in a table and it cannot be null and it will not allow duplicate values.

Create Table EmpTemp
(
      Code numeric(10) constraint pk_primary primary key
)

B.   UNIQUE
This constraint is to ensure that we are not going to insert a duplicate value.
Create Table EmpTemp
(
       Code numeric(10) constraint uc_constraint unique
      
)

C.   NOT NULL
This constraint is to that the column is not going to accept null values.
Create Table EmpTemp(
       Code numeric(10) constraint uc not null
)

D.   Check
This constraint is to ensure that the columns are going to check for specific values or values within ranges.
Create Table EmpTemp
(
       Code numeric(10) constraint check1 check (code between 2000 and 5000),
       Job varchar(20) constraint check2 check (job in ('MANAGER','ANALYST'))

)

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