PHP Check mysqli_num_rows not working - php

Question

I've searched thoroughly and nothing seems to be working; I have this code here which posts into my database but the problem is I am trying to run a conditional which checks if a row exists using the mysqli_num_rows function, but it is not actually working. I have tried many different versions and other functions as well such as mysqli_fetch_row, but nothing seems to work. Here is my code:
if (!empty($_POST)) {
$db_conx="";
$name = $_POST['name'];
$module = $_POST['module'];
$secret = $_POST['secret'];
$uid1 = $dmt->user['uid'];
$queryA = "INSERT INTO table_a (uid1,name,module,secret) VALUES ('$uid1','$name','$module','$secret')";
$resultA = mysqli_query($db_conx,$queryA);
$queryB = "SELECT 1 FROM table_a WHERE name='$name' LIMIT 1";
$resultB = mysqli_query($db_conx,$queryB);
$resultC = mysqli_query($db_conx,$queryB);
$query = mysqli_query($db_conx,"SELECT * FROM table_a WHERE name='$name'");
if (empty($name)||empty($module)||empty($secret)) {
echo "Oops! Can't leave any field blank <br />";
exit();
} elseif(mysqli_num_rows($query) > 0){
echo "name already exists.";
exit();
} elseif ($db_conx->query($queryA) === TRUE) {
echo "New record created successfully.";
exit();
} else {
echo "Error: " . $queryA . "<br>" . $db_conx->error;
exit();
}
}
As you can see the query appears to run but indeed does not do what it's told.

Answer 1

The first line of code inside your IF is destroying the variable you are using to hold the database connection
if (!empty($_POST)) {
$db_conx=""; // get rid of this line
So basically nothing using the mysqli API will work.
ALSO:
Add these as the first 2 lines of a script you are trying to debug
<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
as you are obviously not readng your php error log