Data Integrity In SQL Server


For many businesses, their data is the backbone of their operation. It can be used for analysis, decision making, and communication between staff members. Without a strong understanding of what Data Integrity means, businesses may not be able to effectively manage their data or protect it in case something happens to it. DBAs and data developers must pay high attention to data integrity. This article is for DBAs and data developers who work with SQL Server. In this article we'll discuss what Data Integrity is, why it's important, and how we can make sure to maintain and implement Data Integrity in SQL Server.

Data Integrity in SQL 

Data Integrity is used to maintain the accuracy and consistency of data in a table.

Classification of Data Integrity

  1. System/Pre-Defined Integrity
  2. User-Defined Integrity
Classification of Data Integrity

System/Pre-Defined Integrity

We can implement this using constraint. This is divided into three categories.

System/Pre Defined Integrity 

Entity Integrity

Entity integrity ensures each row in a table is a uniquely identifiable entity. We can apply Entity integrity to the Table by specifying a primary key, a unique key, and not null.

Referential Integrity

Referential integrity ensures the relationship between the Tables.

We can apply this using a Foreign Key constraint.

Domain Integrity

Domain integrity ensures the data values in a database follow defined rules for values, range, and format. A database can enforce these rules using Check and Default constraints.


Constraints are used for enforcing, validating, or restricting data. Constraints are used to restrict data in a Table.

Constraints in SQL Server



Default Constraint is used to assign the default value to a particular column in the Table.

By using this constraint we can avoid the system-defined value from a column while the user inserts values in the Table.

A Table can contain any number of default constraints.

Default constraints can be applied to any datatypes.


Create table Demo(Id int,name varchar(50),Salary int default 15000)  


Unique constraints are used to avoid duplicate data in a column but accept null values in the column. 

It also applies to any data type.

A Table can contain any number of unique constraints.

Create table demo1(id int unique,name varchar(50),price int unique)  

Not Null

It avoids null values from column-accepted duplicate values.

It can apply to any data type.

A Table can contain any number of not null constraints.


Create table Demo2(id int not  null, age int)  

Important Points to Remember

Unique and Not Null constraints have their own disadvantage, that is accepting null and duplicate values into the Table. So to overcome the above drawbacks we write the combination of Unique and Not Null on a column.


Create table demo 3


It is used to verify or check the values with the user-defined conditions on a column.

It can apply to any data type.

A Table can contain any number of Not Null constraints.


Create table demo4(id int, Age int check(Age between 18 and 24))  

Primary key

The primary key adds features of unique and not null constraints.

By using the primary key we can avoid duplicate and null values for the column.

It can apply to any datatype like int, char, etc.

A table can contain one primary key only.


Create table demo5(id int primary key, salary money)  

Composite primary key

If a primary key is created on multiple columns the composite key can apply to a maximum of 16 columns in a table.


create table demo6(id int,name varchar(50),primary key(id,name))  

Important points to remember,

  1. We can apply only a single primary key in a Table.
  2. We can apply the primary key constraint on multiple columns in a Table.
  3. The primary key is also called the composite key and candidate key.

Foreign Key

The most important part of the database is to create the relationship between the database Table.

The relationship provides a method for linking data stored in two or more Tables so that we can retrieve data in an efficient way and verify the dependency of one table's data on another Table.

Important Rules to Create Foreign Key Constraints

In order to create a relation between multiple tables, we must specify a Foreign key in a Table that references a column in another Table which is the primary key column.

We require two tables for binding with each other and those two tables have a common column name and those columns should be the same data type.

  • If a table contains a primary key then it can be called a parent Table.
  • If a Table contains a foreign key reference then it can be called a Child Table.

We can apply the foreign key reference on any datatypes.

By default foreign key accepts duplicate and null values.

We can apply a maximum of 253 foreign keys on a single table.

Step 1

Create table employee(id int primary key,name varchar(50),age int)  

Step 2

Create table company(email varchar(50),address varchar(50),id int primary key foreign references employee(id))  

Now, check the relation between the two tables. Click the database name, click database diagrams, click on new database diagrams, and select the table employee and company and see the relationship between these tables.

Relation Between Tables 

If we want to delete or update the record in the foreign key child table then we need to follow some rules.

For delete

It is used to delete key values in the parent table which is referenced by the foreign key in other tables. All rows that contain those foreign keys in the child table are deleted.

For Update

It is used to update a key value in the parent table which is referenced by the foreign key in another table. All rows that contain the foreign keys in the child table are also updated.

Using the Foreign key we can maintain three types of relationships,

  1. One to one 
  2. One to many 
  3. Many to many 

One-to-One Relationship

A row in a Table associated with a row in the other Table is known as one to one relationship.

One-to-many or many-to-one Relationship

A row in a Table associated with any number of rows in the other Table is known as a one-to-many relationship.

Many to many relationships

Many rows in a table are associated with many rows in the other Table. This is called a many-to-many relationship.

Let's learn more about the importance of integrity. 

Data Integrity is a crucial aspect of data management.

Data integrity is the ability of a database to accurately represent the real world. It's the quality of data that is free of errors and can be trusted. Data integrity is a cornerstone of good data management, and it’s what makes your company’s data accurate, reliable and secure.

A lack of data integrity can be disastrous for any business that relies on access to unchanging data.

Data is important to any business, and it’s critical that the data you keep is accurate, consistent, and complete. Data Integrity is the quality of your data in terms of its accuracy, completeness, and consistency. Data can become corrupted or changed unintentionally at any point during its lifecycle. For example:

  • When one person enters an order into your system, it might get entered incorrectly by someone else who doesn't know how to spell "eggnog."

  • If a database administrator (DBA) makes an error when configuring the database schema you're using for all your application's tables and columns (or worse yet—has no idea what they did because they just copied those settings from another environment), then when you try to run queries against those tables' contents they'll either give you bad results or crash altogether!

  • Even if no one makes any mistakes with actual numbers like dollar amounts or percentages; if someone types in something incorrectly like "1" instead of "January," then it could cause problems later on down the line when someone tries comparing data sets based on date ranges (like comparing orders placed before January 1st against orders placed after January 1st). That would lead them astray because those two dates actually don't match up because one was typed incorrectly!

To maintain data integrity, a variety of practices should be adopted by all businesses that rely on the integrity of their data.

To maintain data integrity, a variety of practices should be adopted by all businesses that rely on the integrity of their data. Data Integrity is important for ensuring accuracy, consistency and security.

If you rely on your company’s data to make decisions, you need to take steps to ensure that your data is accurate and consistent. Maintaining the integrity of your company's information will protect it from corruption or changes by malicious users.

It's equally important for companies with sensitive information about customers to ensure that physical access to that information is restricted appropriately.

Data Integrity shouldn't be confused with Database Integrity.

While the two concepts are related, Data Integrity is a broader term than Database Integrity. Data Integrity concerns itself with the accuracy, consistency and trustworthiness of data in a system. The concept of Database Integrity is concerned with the security of a database, as well as its internal validity (i.e., whether it contains valid information). It also refers to certain aspects of performance and availability; however, these often relate back to issues with security or data quality.

Data Integrity is very closely related to security.

Data integrity is very closely related to security. In fact, the two terms are often used interchangeably. However, while they're similar in some ways, they're not exactly the same thing. Data integrity refers to the quality of your data and how it's stored by your company—but not necessarily how it's accessed by customers or other users. It also doesn't have anything to do with encryption, which is another important factor in protecting sensitive information from unauthorized access.

In other words: data integrity focuses on making sure that your information is accurate and consistent across all platforms—including any third-party apps or services you use as part of your business operations—and that it remains secure from hackers and other malicious actors who might be looking for an opportunity to steal sensitive client information through nefarious means (like ransomware).

Data Integrity is important to ensure that critical information remains accurate and untouched.

Data integrity is a crucial aspect of data management. This means that, when you need to access or manipulate a piece of information, you have confidence that the information will be unchanged and accurate. A lack of data integrity can be disastrous for any business that relies on access to unchanging data. To maintain data integrity, a variety of practices should be adopted by all businesses that rely on the integrity of their data.


In this blog, we learned about Data Integrity in SQL Server.

The best way to understand the importance of data integrity is to imagine what would happen if it wasn't there. A lack of data integrity can cause all kinds of problems, from lost revenue due to poor customer service through inaccurate billing records, or even legal issues as a result of poor record keeping! By making sure that your company's data is always up-to-date and well maintained, you can ensure that your business operates smoothly while also protecting yourself against costly mistakes

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