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.
 
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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:
 

 
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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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