Cant able to update table from different database table mysql in php

Question

I cant able to Update my users table from different college table which is present in another main database. But my query running successfully on mysql but when I am trying to execute query using PHP it cant able to update the user database from the college database

    UPDATE users 

     SET 

     student_name = ( SELECT main.college.Student_Name
                       FROM main.college
                       WHERE main.college.Enroll_No =  '123456'
                       LIMIT 1 ) 
      WHERE user_id =5

Above query successfully running on phpmyadmin. But in PHP cant able to Update the user table

<?php



         require_once('dbConnect.php');

            $sql = "UPDATE users \n"
                    . "\n"
                    . "SET \n"
                    . "\n"
                    . "student_name = ( SELECT main.college.Student_Name\n"
                    . " FROM main.college\n"
                    . "WHERE main.college.Enroll_No = '123456'\n"
                    . "LIMIT 1 ) \n"
                    . "WHERE user_id =5";
                   if(mysqli_query($con,$sql)){

                             mysqli_query($con,$sql);

                             echo 'successfully registered';
            }else{
                echo 'oops! Please try again!';
            }


     mysqli_close($con);

?>

Answer 1

The code appears to be calling the mysqli_query function two times, which is not necessary.

For debugging, I strongly recommend that you call mysqli_error (in the else block) to retrieve the MySQL error message, and echo that out. (That would let you see an error, rather that wondering what the problem is.

Also for debugging, echo out the contents of $sql before you send it to the database.

---

(We're assuming that the behavior you observe is the echo of 'oops! Please try again!'. But that's really just a guess, since the description of the behavior you observe is a rather vague "cant able to".)