php - Warning: mysqli_fetch_row() expects parameter 1 to be mysqli_result, boolean given in -

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• mysqli_fetch_array()/mysqli_fetch_assoc()/mysqli_fetch_row() expects parameter 1 resource or mysqli_result, boolean given 33 answers

i know there's been threads it, didn't me. anyways i'm new in php , creating login system when got stuck. can't understand why giving me error: warning: mysqli_fetch_row() expects parameter 1 mysqli_result, boolean given in

code here:

<?php session_start();  if(isset($_post['username'])){      include_once("dbconnect.php");      $usname = strip_tags($_post["username"]);     $paswd = strip_tags($_post["password"]);      $usname = mysqli_real_escape_string($dbcon, $usname);     $paswd = mysqli_real_escape_string($dbcon, $paswd);      $paswd = md5($paswd);      $sql = "select id, fooruminimi, password liikmed username = '$usname' , aktiveeritud = '1' limit 1";     $query = mysqli_query($dbcon, $sql);     $row = mysqli_fetch_row($query);     $uid = $row[0];     $dbusname = $row[1];     $dbpassword = $row[2];      if($usname == $dbusname && $paswd == $dbpassword){         //sessioni avamine         $_session['username'] = $usname;         $_session['id'] = $uid;         //suunamine         header("location: user.php");            }     else{         echo "<h2> vale kasutajanimi või parool!</h2>";     } } ?> 

this occur 2 main reason

1. mysqli_connect() failed connect
2. mysqli_query() return nothing

check in code

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

and check $sql returns data

$sql = "select id, fooruminimi, password liikmed username = '$usname' , aktiveeritud = '1' limit 1";