How to Check if Value Exists in a MySQL Database

In this tutorial, we are going to see how to check if a value exists in a MySQL database. The IN operator allows you to check whether a specified value matches a value in a set of values or values returned by a subquery.
 

Syntax:

The syntax of the IN operator in MySQL:

expression IN (value1, value2, ...., valueN);

Let’s take a few examples of using the IN operator to see how it works. For this we will use the “Clients” table.
 

 

 
Now let’s assume, based on the above Clients table, that you want to display clients with age equal to 20, 22 and 24. This can be done as follows:

SELECT *
FROM Clients
WHERE Age IN (20, 22, 24);

 

Using the IN operator with a subquery:

The IN operator is often used with a subquery. Instead of providing a list of literal values, the subquery gets a list of values from one or more tables and uses them as input values for the IN operator.

Consider the following “Orders” table:
 

 

 
For example, if you want to find orders whose clients are older than 30, you use the IN operator, as shown in the following query:

SELECT    
    OrderNbr, 
    Totale
FROM    
    Orders
WHERE ClientID IN
(
     SELECT 
         ClientID
     FROM 
         Clients
     WHERE Age > 30
);

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