save data into database in wordpress frontend code example

Example: wordpress query to save in database

<?php
    if (!empty($_POST)) {
        global $wpdb;
        $table = 'contact_form';
        $data = array(
            'names' => $_POST['yourname'],
            'emails'    => $_POST['customer_email'],
            'gender' => $_POST['customer_gender'],
            'age' => $_POST['customer_age']
        );
        //echo "<pre>"; print_r($data);

        $success=$wpdb->insert( $table, $data );
        if($success){
            echo 'data has been save' ; 
        }
    } else {
    		echo "data not save";
    	}
        ?>
        <div class="container">
        	<div class="row ">
        		<div class="col-md-12 pb-5">
			        <form method="post">
			            Your name:<input type="text" name="yourname" id="yourname">
			            Your Email:<input type="text" id="customer_email" name="customer_email"/><br>
							Gender:<input type="radio" name="customer_gender" value="male">Male
								   <input type="radio" name="customer_gender" value="female">Female<br>
						    Your Age:<input type="text" name="customer_age" id="customer_age"><br>
						    <input type="submit" name="submit" value="Submit">
			        </form>
		        </div>
	        </div>
	    </div>