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Difference between Exist and Not-Exist Operator

This article discusses the most important features of SQL's Exist and Not-Exist Operators and shows their syntax, utility, and use cases.

Difference between Exist and Not-Exist Operator


Structured query language (SQL) has become the standard language for manipulating data and, namely, for parsing out data in relational databases. To run various data-related operations, SQL uses a multitude of different operators and functions. The performance of exist and not-exist operators is vital to developing complex queries. They are especially helpful functions when using subqueries and conditional data retrieval. Thorough knowledge of exist and Non-exist operators is an essential skill for database administrators and SQL developers, as they must identify the subtle meaning between these two operators.

Overview of Exist Operator:

The exits operator in SQL is almost always used to verify whether the elements of a subquery are present or not. The system makes this prior determination so that it can decide whether a subquery returns any rows or whether they Exist operator is to be returned as True or False. A subquery frequently serves as a deciding character when associating outer query data with an exist operator.


Suppose a SQL query that returns a result set which is legitimately used as a subquery in the exist clause. In that case, either a list or a single object in the subquery can match the SQL statement that invokes the exist clause.


This query allows the employee ID list of people who have at least one order registered to be retrieved by this example.

Overview of Not-Exist Operator:

However, the SQL Not-Exist operator supports the approach of the Exist one, functionally contrasting with it. It wants to find out that a subquery doesn't have any rows. In the case of the Not-Exist operation, the result is true if the subquery has no rows and false if it has any rows. The Not-Exist operator is typically utilized for data that are correlated in such a way that they allow conditional data retrieval just as they Exist operator does.


The subquery inside the Not-Exist clause can be any valid SQL query that produces a result set, much like the Exist operator.


In this case, the search request gives back the names of employees whose names are not supported by orders.

Differences between Exist and Not-Exist Operators:

Let's now examine the main distinctions between SQL's Exist and Not-Exist operators:

1. Criteria for Evaluation:

  • Not-Exist Operator: Returns false if the subquery returns no rows and returns true otherwise.
  • Exist Operator: This operator tests whether any sub queries hold at least one record or not. This can be performed by checking if the subquery is either true or otherwise false.

2. Conditional Logic:

  • Exist Operator: This operator is supportive of writing a correlated subquery. It picks rows according to the previous row if the related row exists.
  • Not-Exist Operator: It is something that detects rows in a recursive subquery and gives you a choice based on the fact that there are no associated entries.

3. Outcome Set:

  • Exist Operator: Generates rows flagged as a result of the Where clause.
  • Not-exist operator: It returns a row whenever the condition is not satisfied in the Not-exist clause.

4. Aspects of Performance to Consider:

  • Exist Operator: Although the database engine usually does not allow such a union operation optimization, the situation can change sometimes. The engine becomes capable of terminating subquery processing as fast as a single matching row is found.
  • Not-Exist Operator: These operators that historically impact performance more, particularly with in large datasets, since it may need to scan the entire subquery result for no evaluations.

Practical Applications:

In SQL queries, the Exist and Not-Exist operators can behave nicely in their way.

  • Exist Operator: Before the action is taken, all the existing data in the base must be reviewed. This may include adding, modifying, or removing data.
  • Not-Exist Operator: It involves creating codes that lack data or have incomplete data.
  • Writing off the records that emerge from subqueries of the table queries, which are irrelevant to each other.

Fulfilling the eventful condition agendas, which are achieved when a set of default requirements are satisfied.

Performance Optimization:

  • Exist Operator: The query optimizer is enabled to scan indexes for Exist operator as well.

In the course of working with very extensive datasets, it might yield more proficient execute-query-plans than others say, COUNT(*), JOIN.

  • Not Exist Operator: The efficacy of a query optimizer in a database engine considerably affects the performance of the Not-Exist operator.

Developers using the Not-Exist operator should be aware of the lengthy subqueries. They give rise to expensive joins and full table scans, which ultimately lead to slow performance.

Correlated Subqueries:

Exist Operator:

  • Two main operators are involved in the correlated sub-queries when the inner query is related to the inner columns of the outer query.
  • This provides a powerful access control instrument for conditional data transfers by letting out only relevant rows of the inner query based on the presence of the respective rows of the outer query.

Not-Exist Operator:

  • For example, in order to do non-correlated subquery rows, entries in the outer query that cannot be found in the inner query are often discovered with the Not-Exist operator.
  • Another task a database professional could perform is searching for records with incomplete or incorrect data or SQL queries with exclusionary logic.

Use Cases and Examples:

Exist Operator:

  • Use case: Make sure that a preliminary study has been done before beginning any operation.

This can be demonstrated by instituting a mandatory verification of membership for at least one that is still valid for people who wish to access premium facilities or payment of 10% transaction fees.

  • Use case: Decision-making based on the relation of the received message using the ultra-health care information.

Furthermore, we may even use all the items that have at least one review.

Not-Exist Operator:

  • Use case: It is difficult to identify the data that is there partially or is missing frequently.

Example: Listing all employees that have yet to be added to a project.

  • Use case: As reason goes against exclusion. Discovering the voice of visitors to a creative exhibition can offer valuable insights into their experiences, perspectives, and emotions. By actively listening and engaging with the public, organizers, and curators can gain a better understanding of how the artwork resonates with individuals, the impact it has on their lives, and how it affects their overall perception of the exhibition. Through this process, the participation of visitors becomes

Example: Just because the client hasn't bought anything in the last month does not mean that we shouldn't choose her as a customer.

Best Practices:

  • Exist Operator: To return a result set that includes 0 or many associated records, use the existing operator.

Ensure that all necessary indexes are formed and do not apply several subqueries, as this will improve search optimization for search queries that contain operator(s).

  • Not-Exist Operator: Subquery inside NOT-EXIST operator and big subqueries performance problems can be prevented by using a cautious approach.

In cases where it is necessary, it would be helpful to work with LEFT JOINs to contradict to get a faster response.


Thus, Exist and Not-Exist operators allow SQL to find and bring together conditional data and, therefore, serve as highly effective tools. The not-exist operator ensures that records are missing from subqueries, while the Exist operator lets you know if records in subqueries are present. Building correct SQL queries with the distinct differences between these operators in these determinations is mostly involved, in particular when the subqueries, which are related, and complex data filtering reasons are concerned. SQL developers and database administrators can heighten the operational efficiency of their database jobs as well as create fast-performing databases by mastering existing (and existing) operators. This will result in super data management and analytics reports.

FAQs on exist and non-existent operators:

The following are some frequently asked questions (FAQs) about SQL's Exist and Not-Exist operators:

SQL is the database's query language. What does Exist operator mean in the context of SQL queries?

To check the presence of qualifying rows in a subquery, we will use SQL's Exist operator. If the subquery results in the leading row, TRUE is returned, otherwise, FALSE is returned.

How to write the exits operator syntax?

The following is the syntax for using the Exist operator in SQL:

SQL code:

From the point of view of the SQL queries, how does the Exist operator usually work?

As a subquery implies a dependence of its outcome on data from an outer query, it is a common approach to use the Exist operator. It is used to trim rows' concerning subqueries containing rows or not.

What does the SQL Not-Exist operator serve?

SQL query operators, such as the Exist operator and the Not-Exist operator, operate oppositely. When the subquery gets no rows, it gives true, but if it gets other rows, it gives false.

In what way can the Not-Exist operator be employed in a syntax?

The following is the SQL syntax for using the Not-Exist operator: The following is the SQL syntax for using the Not-Exist operator:

SQL code:

What are the typical uses of the Not-Exist operator?

Detecting empty data in records or records that are linked with sub-queries and not having relevant associated records falls within the operators' responsibility of Not-Exist, also known as Delete from (the non-association of particular records).

What is the difference in performance between the exist as well as not-exist Operators?

Sizing of the set, search optimization, database indexing, etc, are all factors that will determine the performance of Exists and Not-Exists. The data storage engine could sometimes not be able to find an alternative, higher performance way of optimizing sub-query searches that are wrapped by the Exist operator rather than the Not-Exist operator, which could be another reason why performance may be slower-especially when dealing with huge data and they all need to be scanned from the result set for sub-query searches or the whole dataset.

When utilizing Exist and Not-Exist operators, are there any recommended practices to follow?

The best ways to use the Exist and Not-Exist operators are to optimize searches by ensuring the right indexing, eliminating unnecessary subquery nesting, and using caution when using the Not-Exist operator with huge subqueries to prevent performance problems.

These FAQs summarize the main ideas and factors in SQL to help users better understand the use and implications of the exist and not-exist operators.

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