SQL Not Equal: Everything You Need to Know

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Learning and practicing SQL implies remembering a wide array of keywords. Keywords and various commands are the essences of SQL, to be precise. When it comes to various SQL commands, the data manipulation statements hold a superior position. Various commands like WHERE, UPDATE, etc., belong to DML and are reserved keywords in SQL. 

We cannot overlook the comparison operators when discussing different DML statements, especially “not equal.” You are required to understand the not equal (!=) operator if you wish to grasp the DML commands in detail. Despite being one of the most fundamental commands, users tend to make numerous mistakes when using the not equal operator in SQL, especially the beginners. All these happen due to a lack of knowledge about the specific comparison operator.

However, you need not worry anymore! If you have been struggling with the not equal operator in SQL to date, here is the ultimate resource for you to follow. Below you will get everything that you must know about SQL not equal. Let’s proceed step by step and become well-acquainted with the Not Equal operator.

What are DML Commands?

Before understanding the not equal operator in SQL, you need to clear your concepts regarding the DML commands. So, let’s dive in!

Abbreviated as DML, the data manipulation language holds numerous commands that drive the query results. Unlike data definition language, users leverage DDL commands to find patterns, derive specific tuples, and get relevant answers to any queries regarding the database. 

Various statements like UPDATE, INSERT, DELETE, and LOCK belong to the DML class. Apart from these commands, DML includes numerous operators like arithmetic and comparison operators. For instance, ‘+,’ ‘/,’ and ‘!=’ are some operators in data manipulation language.

What are Comparison Operators in SQL?

Now that you know the meaning of Data Manipulation Language, you must be intrigued to understand comparison operators. Also, you require the knowledge of comparison operators in SQL to grasp the not equal operator afterward. So, let’s quickly go through the meaning of comparison operators!

SQL derives the concept of comparison operators from mathematics. As these operators compare two values in arithmetic, they are used to test the inequality between two expressions in SQL. 

The comparison operators have boolean values as their return type. TRUE, FALSE, and UNKNOWN are the reserved keywords that comparison operators in SQL use as results after testing the inequality between two expressions. These operators return UNKNOWN when either or both the expressions have a NULL value.

What is SQL Not Equal Operator?

As you already know, Data Manipulation Language has a superior position among all commands in SQL. The Not Equal statement belongs to the class of comparison operators in DML. 

So, what do you mean by Not Equal in SQL? Symbolized as ‘!=,’ the Not Equal command in SQL is an operator that compares two expressions and returns a boolean value. It returns TRUE if the two sides are unequal and FALSE when both the expressions are equal. All in all, you can use the Not Equal operator to compare the non-equality between two terms in SQL.

The Not Equal operator is used with several other commands in SQL like WHERE. Now, let’s understand some examples to understand the SQL Not Equal command better.

Examples to Understand SQL Not Equal Operator

We are already through the theoretical meaning of the Not Equal operator in SQL. Now, let’s clear the concepts with some examples discussed right below.

  1. Students Database

Suppose we have a ‘students’ relation (table) comprising student ID (stud_id), name (stud_name), course enrolled (course), and stream. Now, you wish to run an SQL query on the database to find out the details of the students not enrolled in the ECE department of the college. You can use the Not Equal operator to write an SQL query and get the desired output. Here is what you can write:


FROM students

WHERE stream != ‘ECE’;

The ‘!=’ operator looks for tuples where the stream attribute does not equate to ECE. So, the above query will return all the tuples (rows) that do not have ‘ECE’ as the stream.

2. Employees Database

You have an ’employees’ relation with various fields like employee ID (emp_id), their names (emp_name), department (dept), and much more. Now, you want to get the details of all employees not working in the sales department. So, you can write a query involving the SQL Not Equal operator to get the desired tuples. Below is the SQL query to perform the required action:


FROM employees

WHERE dept != ‘sales’;

That’s it! The ‘!=’ operator here returns TRUE where the department is not equal to sales. S, the above query runs to display the details of all the employees not working in the sales department.

Besides, you can find more applications of the not equal operator in SQL. You can use it with almost all databases where you require eliminating some tuples based on the values of attributes.

Difference Between ‘!=’ and ‘<>’

When studying the Not Equal operator in SQL, you can find several instances where the corresponding symbol is written as ‘<>’ and not ‘!=’. Now, what’s the difference between the two symbols? Before understanding their differences, let’s go through their similarities.

Although written differently, both ‘<>’ and ‘!=’ refer to the same operator, that is, Not Equal in SQL. Also, you can interchange the symbols in a SQL database query without affecting the results. So, these symbols are almost similar, and you can freely use either of them. 

Since the two symbols are written differently, they must have some differences that you should know. Although both operators give the same output, a difference occurs when considering the ISO standards. The operator ‘<>’ follows the ISO standards. So, book authors prefer using ‘<>’ to improve the standard of their writing. However, ‘!=” does not align with the ISO guidelines.

That was all about the Not Equal operator in SQL. The fundamental operator has a special place in the DML umbrella, and users often leverage it in their queries. Congratulations! You’ve grasped the SQL Not Equal command by now.


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