SQL - IN vs EXISTS

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In SQL, we use the IN operator to simplify queries and reduce the need for multiple OR conditions. It allows us to match a value against a list of values. On the other hand, the EXISTS operator checks whether one or more rows exist in a subquery and returns either true or false based on this condition. If the subquery finds at least one row, the EXISTS operator returns true; otherwise, it returns false.

The SQL IN Operator

The IN operator in SQL is used to check if a particular value matches any within a given set. This set of values can be specified individually or obtained from a subquery. We can use the IN operator with the WHERE clause to simplify queries and reduce the use of multiple OR conditions.

Suppose we have a table named CUSTOMERS and we want to retrieve customer details based on their IDs. In this scenario, we can use the IN operator with the WHERE clause to fetch the details of these specific IDs.

Syntax

Following is the syntax of the SQL IN operator −

SELECT column_name
FROM table_name
WHERE column_name
IN (value1, value2, valueN);

In the above syntax, the column_name matches every value (value1, value2, ... valueN). If the matches occur, The IN operators returns true; otherwise, false.

Example

First of all, let us create a table named CUSTOMERS using the following query −

CREATE TABLE CUSTOMERS (
   ID INT NOT NULL,
   NAME VARCHAR (20) NOT NULL,
   AGE INT NOT NULL,
   ADDRESS CHAR (25),
   SALARY DECIMAL (18, 2),       
   PRIMARY KEY (ID)
);

Now, add records into the above created table using the INSERT INTO statement as shown below −

INSERT INTO CUSTOMERS VALUES 
(1, 'Ramesh', 32, 'Ahmedabad', 2000.00),
(2, 'Khilan', 25, 'Delhi', 1500.00),
(3, 'Kaushik', 23, 'Kota', 2000.00),
(4, 'Chaitali', 25, 'Mumbai', 6500.00),
(5, 'Hardik', 27, 'Bhopal', 8500.00),
(6, 'Komal', 22, 'Hyderabad', 4500.00),
(7, 'Muffy', 24, 'Indore', 10000.00);

The table will be created as follows −

The following query retrieves the NAME and SALARY columns from the CUSTOMERS table for rows where the ID is 1, 2, or 3.

SELECT NAME, SALARY FROM CUSTOMERS WHERE ID IN(1, 2, 3);

Output

On executing the query above, the output is displayed as −

The SQL EXISTS Operator

The EXISTS operator is used to look for the existence of a row in a given table that satisfies a set of criteria. It is a Boolean operator that compares the result of the subquery to an existing record and returns true or false.

The returned value is true, if the subquery fetches single or multiple records; and false, if no record is matched. EXISTS operator follows the querys efficiency features, i.e. when the first true event is detected, it will automatically stop processing further.

We can use the EXISTS operator with the SELECT, UPDATE, INSERT and DELETE queries.

Syntax

Following is the basic syntax of SQL EXISTS operator −

SELECT column_name FROM table_name
WHERE EXISTS (
   SELECT column_name FROM table_name
   WHERE condition 
);

Example

First of all, consider the CUSTOMERS table, and create another table named EMPLOYEES using the following query −

CREATE TABLE EMPLOYEES (
   EID INT NOT NULL,
   NAME VARCHAR (20) NOT NULL,
   AGE INT NOT NULL,
   CITY CHAR (25),
   CONTACT INT,       
   PRIMARY KEY (EID)
);

Now, let us insert some records into the EMPLOYEES table using the INSERT INTO statement as shown below −

INSERT INTO EMPLOYEES VALUES 
(1, 'Varun', 32, 'Ahmedabad', 12345),
(2, 'Mahesh', 22, 'Kashmir', 34235 ),
(3, 'Suresh', 43, 'Kerala', 12355 );

The table will be created as follows −

In the following query, we are using the EXISTS operator to fetch the names and ages of CUSTOMERS whose AGE is same as the AGE in the EMPLOYEES table.

SELECT NAME, AGE 
FROM CUSTOMERS 
WHERE EXISTS(
   SELECT * FROM EMPLOYEES 
   WHERE CUSTOMERS.AGE = EMPLOYEES.AGE
);

Output

Following is the output of the above query −

IN vs EXISTS

Following table summarizes all the differences between IN and EXISTS −