Understanding the Concept of “IS NULL” in SQL Server

Dear Dev, whether you are a beginner or an experienced SQL Server user, you might have come across the term “IS NULL”. It is a conditional operator that is used to check whether a value is NULL or not. In this journal article, we will explore the concept of “IS NULL” in SQL Server in detail. Let’s dive into the details!

What is NULL and Why is it Important in SQL Server?

In SQL Server, NULL is a special value that represents the absence of any data or unknown value. It is not the same as zero or an empty string. NULL values can be present in any data type, including string, integer, date, and others. Understanding NULL in SQL Server is essential because it can impact how you write and use queries.

In SQL Server, NULL values can be used to represent:

• A missing value in a record
• An unknown value that we cannot determine
• A value that is not applicable or undefined

Let’s take a look at an example:

ProductID	ProductName	ProductPrice	ProductCategory
1	Mobile Phone	1000	Electronics
2	Laptop	2000	Electronics
3	Headphones	NULL	Electronics
4	Backpack	50	Accessories

In the above table, the ProductPrice of Headphones is NULL because we do not have the information available. This is an example of undefined or missing information, and we can represent it with NULL values.

What is “IS NULL” in SQL Server?

“IS NULL” is a keyword that is used to check whether a value is NULL or not. It returns a Boolean value – TRUE if the value is NULL, and FALSE if it is not NULL. You can use “IS NULL” in combination with WHERE and HAVING clauses to filter out the NULL values.

Let’s take an example:

SELECT ProductName FROM Products WHERE ProductPrice IS NULL;

The above query will return all the products whose ProductPrice is NULL.

How to Use “IS NULL” in SQL Server?

The syntax for using “IS NULL” in SQL Server is straightforward:

SELECT column_name(s) FROM table_name WHERE column_name IS NULL;

You can use “IS NULL” in combination with other operators like ‘AND’, ‘OR’, and ‘NOT’ to create complex queries. Here are a few examples:

SELECT ProductName FROM Products WHERE ProductPrice IS NULL AND ProductCategory=’Electronics’;

The above query will return all the products whose ProductPrice is NULL and belong to the Electronics category.

SELECT ProductName FROM Products WHERE NOT ProductPrice IS NULL;

The above query will return all the products whose ProductPrice is not NULL.

Common Mistakes to Avoid When Using “IS NULL”

When using “IS NULL” in SQL Server, it’s essential to avoid these common mistakes:

• Not using ‘IS NULL’ explicitly – using ‘=NULL’ instead
• Forgetting to use parentheses when combining ‘IS NULL’ with other operators
• Not using the correct data type for NULL values

Not Using ‘IS NULL’ Explicitly – Using ‘=NULL’ Instead

Using ‘=NULL’ instead of ‘IS NULL’ is a common mistake that beginners make in SQL Server. Remember that ‘=’ is an assignment operator and is used to assign a value to a variable. On the other hand, ‘IS NULL’ is a conditional operator and is used to check whether a value is NULL or not.

SELECT * FROM Products WHERE ProductPrice = NULL;

The above query is incorrect and will not return any results because it’s using ‘=’ instead of ‘IS NULL’.

Forgetting to Use Parentheses When Combining ‘IS NULL’ with Other Operators

When combining ‘IS NULL’ with other operators like ‘AND’, ‘OR’, and ‘NOT’, it’s important to use parentheses correctly to ensure that the query logic is correct.

SELECT * FROM Products WHERE ProductPrice IS NULL OR ProductCategory = ‘Electronics’;

In the above query, the parentheses are not used correctly, which can lead to incorrect results. The correct query should be:

SELECT * FROM Products WHERE (ProductPrice IS NULL) OR (ProductCategory = ‘Electronics’);

Not Using the Correct Data Type for NULL Values

NULL values can be present in any data type in SQL Server. However, it’s essential to use the correct data type when working with NULL values. For example, if a column is of type INT, it cannot store NULL values. Instead, you should use the data type INT NULL.

FAQ

Q1. What is the difference between NULL and an empty string in SQL Server?

A. In SQL Server, NULL represents the absence of any data or an unknown value, while an empty string represents a string with zero length. NULL is not the same as an empty string because an empty string is still a value, while NULL is the absence of any value.

Q2. Can I use “IS NULL” with aggregate functions in SQL Server?

A. Yes, you can use “IS NULL” with aggregate functions like SUM, AVG, COUNT, and others in SQL Server. For example:

SELECT COUNT(*) FROM Products WHERE ProductPrice IS NULL;

Q3. How do I check whether a value is not NULL in SQL Server?

A. You can use the “IS NOT NULL” operator in SQL Server to check whether a value is not NULL. For example:

SELECT ProductName FROM Products WHERE ProductPrice IS NOT NULL;

Conclusion

In conclusion, understanding the concept of “IS NULL” in SQL Server is essential for writing efficient queries. NULL values can impact how you write and use queries, and using “IS NULL” correctly can help you filter out the NULL values. By avoiding the common mistakes and following the correct syntax, you can write error-free queries that return accurate results. We hope this journal article was helpful and informative for you, Dev!