mysql check if query ran already code example

Example 1: node js check if a user exists in mysql

connectDB.query("SELECT ACCOUNT_ID FROM registration WHERE ACCOUNT_ID = '"+ userAccnt +"'", function(err, result, field){
     if(result.length === 0){
        //new user logic
}else{  
    //existing user, redirect to another page 
 }
        }

Example 2: php check if query succeeded

<?php
	// peform a query 
      $query = "SELECT `*` FROM user";
      $results = mysqli_query($databaseConnection, $query);

      if (mysqli_num_rows($results) == 0) {
        // The query returned 0 rows!
      } else {
        // the query returned ATLEAST one row
      }

      if (mysqli_num_rows($results) >= 5) {
        // the query returned more than 5 rows
        }
?>