Select from multiple MySQL tables

Question

i'm trying to select value from different tables but i face some errors in the result i want to check if there is any values i will echo "Yes" otherwise echo "No"

<?php

if($_SERVER['REQUEST_METHOD']=='POST'){
    $username=$_POST['username'];


    require_once('dbConnect.php');

    $sql="SELECT donator.national_id, needy_people.national_id".
       "FROM donator, needy_people".
           " WHERE donator.national_id='$username' OR needy_people.national_id='$username' limit 50";


    $result=mysqli_query($con,$sql);
    if($check>0){
        while($row=mysql_fetch_array($sql)){

            $check=mysqli_fetch_array(mysqli_query($con,$sql));
        }
    }

    if(isset($check)){
        echo'YES';
    }else{
        echo'Noooo';
    }
    mysqli_close($con);

}else{
    echo'error';
}

can anybody solve this problem help!

Answer 1

When you put as condition if($check>0) , $check is not defined yet, so it won't be processed, hence $check stay unset. Also you should use the empty() function to test existence of values in it

Answer 2

If you're trying to check if a row exists when you run your query consider using the function mysqli_num_rows

if (mysqli_num_rows($result) > 0) {
    echo "Has row";
} 

Answer 3

$count=mysqli_num_rows($check);
if($count>0)
echo "yes";
else
echo "no";