How to Use Integrity Constraints in SQL Server Database Design

In this article we learn about the Integrity Constraints feature in Database design, and how it helps users to safeguard what is entered in the database tables.

SQL Server databases are a storehouse of data, although the access to enter data in the database should be limited to only a few people, there are other measures as well that need to be taken to ensure only relevant data is entered in the tables. One such measure is making use of Integrity Constraints for SQL databases. Integrity constraints are nothing but a set of rules which are used to define what type of data can be entered in the database. A lot of the people think that just defining the cluster index and the primary key of the database in question is enough, but it’s not! You need to make use of integrity constraints as well.Integrity Constraints In SQL Server Database Design

Integrity Constraints in SQL Server

These are provided within the SQL Server database engine and are the most effective solution for checking database integrity. Constraints like UNIQUE, CHECK, DEFAULT, primary key, foreign key should all be defined so that there are no invalid entries made in the database due to undefined constraints. There are two broad categories in which the Integrity Constraints available in SQL Server can be divided, these are:

  • Column Level Constraints – These are the type of constraints that are specified immediately after CREATE TABLE statement is used for column definition.
  • Table Level Constraints – These are those types of constraints that are specified once the ALERT TABLE statement is used for defining all the columns.

Apart from these two broad categories of Integrity Constraints, there are multiple other types of Integrity constraints in SQL Server.

Types of Integrity Constraints in SQL Server

MS SQL Server provides you access to 5 different Integrity Constraints.

  1. Primary Key ConstraintPrimary Key Constraint – In a database, the primary key can be one or more columns from the database table that is used for providing a unique identification number for each record on the table. This constraint ensures that the value is neither duplicate, not null.
  2. Unique Key Constraint – In definition it is pretty much like the primary key constraint, the only difference here is that it can take up to one null value, but no duplicate value.
  3. Foreign Key Constraint – The foreign key field of a database table forms the primary key field for another table, this not only accepts several null values, but also duplicate values.
  4. Not Null Constraints – This is one of those constraints that ensure there are no null values in the columns that have been specified with not null value. It is through this constraint that all rows with a specified condition on no null values never have null values.
  5. Check Constraints – This is one of the general integrity constraints that specifies a given business rule to be applied on any given column of the table, to which all rows must adhere to.

With the help of the five integrity constraints mentioned above, it becomes easier for the user to ensure what goes in the database, and what doesn’t.

Besides investing time in database optimization, DBAs also need to constantly update their business continuity plans. Keeping a tool to repair mdf database files can go a long way in ensuring zero data loss in the event of a SQL crash.

Author Introduction:

Victor Simon is a data recovery expert in DataNumen, Inc., which is the world leader in data recovery technologies, including recover mdb and sql recovery software products. For more information visit

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