在php中显示MySql数据库错误[重复]

How can MySql database errors like 'trying to insert duplicate record' be captured and displayed in PHP?

get this error when inserting -- Warning: mysqli_error() expects parameter 1 to be mysqli, boolean.

In this case i know I'm getting it because I'm trying to insert a duplicate record. does php/mysql not give specific errors? which i could display on screen for end user to understand .

function querydb($sql){

        $con=mysqli_connect("localhost","my_user","my_password","my_db");

            // Check connection
            if (mysqli_connect_errno()) {
              echo "Failed to connect to  Database: " . mysqli_connect_error();
              return 0;
            }

            $result = mysqli_query($con,$sql)  or die("Error in the query.." . mysqli_error($result));
            $con->close();

            return $result;
}

</div>

First turn on the error reporting. Add on top of your file:

error_reporting(E_ALL);

Then if the log doesn't make sense to you, try writing the SQL and pasting it into phpMyAdmin, it'll probably show a different error (if it's being caused by sql).