how to write if condition for multpile queries like - php

Question

I have 3 queries like
$q1 = select email from tbl students
$q2 = select email from tbl corporates
$q3 = select email from tbl institutes
i want check to all 3 tables if email count is zero from all above then only do proceed like that,,
can i write like this:
if(mysqli_num_rows($q1) || mysqli_num_rows($q2) || mysqli_num_rows($q3) ==0){
proceed to process.
}else{
do nothing
}
My question is it a correct way to approach or anything is better left which i need to learn.

Answer 1

you need to use & instead of || and also check rows count for each of your mysql object
if(mysqli_num_rows($q1) == 0 && mysqli_num_rows($q2) == 0 && mysqli_num_rows($q3) ==0){
//proceed to process.
} else {
//do nothing
}

Answer 2

You should execute those queries first so you will have:
$db = mysqli_connect("localhost","my_user","my_password","my_db");
$q1 = "select email from tbl students";
$q2 = "select email from tbl corporates";
$q3 = "select email from tbl institutes";
$db_q1 = mysqli_query($db, $q1);
$db_q2 = mysqli_query($db, $q2);
$db_q3 = mysqli_query($db, $q3);
if(mysqli_num_rows($db_q1) == 0 && mysqli_num_rows($db_q2) == 0 && mysqli_num_rows($db_q3) == 0) {
proceed to process.
}

Answer 3

try can do easier using mysqli_multi_query()
$con=mysqli_connect("localhost","my_user","my_password","my_db");// Check connection
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
$sql = select email from tbl students";
$sql .= select email from tbl corporates";
$sql .= "select email from tbl institutes";
// Execute multi query
if (mysqli_multi_query($con,$sql)){
do{ // Store first result set
if ($result=mysqli_store_result($con)) { // Fetch one and one row
if (mysqli_fetch_row($result) == 0) {
//your code here
}
}
}