php - Revoke User Creation, write to DB -

this small school project. new php & sql. have form, in user enters desired username & password. thereafter, trying check database see whether account same username exists. here code:

$sqlvalidate = "select id useraccounnts username='$username'"; $resultvalidate = $conn->query($sqlvalidate);  $sql = "insert useraccounts values($id, '$username', '$password')";  if ($resultvalidate != 0) {      $date = new datetime(); //this returns current date time     $time = $date->format('d-m-y-h-i-s');      $sqlerrorlog = "insert errorlog (errortype, errortime) values ('failed create new user, username exists', '$time')";     $result = $conn->query($sqlerrorlog);      echo '<script type="text/javascript">'     , 'alert("sorry,an account username exists. please choose one.");     window.location.href = "user.php";'     , '</script>'     ;   } 

firstly, query database. purpose of doing check whether id exists username equal username passed form. thereafter, use if statement checks see whether id is/is not equal 0 (to see whether such id exists). if does, write error log database.

the code doesn't work. ignores if statement , writes new user account database regardless. in advance help. don't mind whether code secure or not, long works.

ps, don't have else statement if statement.

in end decided take approach:

<?php $id=10001; $sql = "select id useraccounts order id desc"; $result = $conn->query($sql);  if ($result->num_rows > 0) { $row = $result->fetch_assoc(); $id = $row["id"] + 1;  }  $username = $_request["emailinput"]; $password = $_request["passwordinput"];  //the following query used check if username same  //name username entered user exists $sqlvalidate = "select id useraccounts username='$username'";   $result = $conn->query($sqlvalidate); //running query  //if query returns results, error inserted db using following code: if ($result->num_rows > 0) {      $date = new datetime(); //this returns current date time     $time = $date->format('d-m-y-h-i-s');      //the following code queries db         $sqlerrorlog = "insert errorlog (errortype, errortime) values ('failed create new user, username exists', '$time')";     $result = $conn->query($sqlerrorlog);      echo '<script type="text/javascript">'     , 'alert("sorry,an account username exists. please choose one.");     window.location.href = "user.php";'     , '</script>'     ;     return; } 

therefore, see whether there id same username. if query returns results (if row such username), revokes request, writes db, , gives javascript alert notify user. works , writes db.