php - MySQLI Update set +1 the correct form and symbols -

edit; there no error , other things work updating no +1 :( nothing gets updated- maybe because using wrong quotes?

i looking on internet people uses following kind of query

update `attempts` set `fails` = fails+1 id='3'" 

i confused because others uses

update `attempts` set `fails` = `fails` +1 id='3'" 

and

update `attempts` set `fails` = +1 id='3'" 

which form correct 1 while inserting mysql , mean symbols used. uses symbols others don´t , makes me confused. questions symbols , correct form when inserting data

just need know correct form when use `` when ' ' , when " " in query only

"please add answer mark correct – cardinale 4 mins ago"

after multiple comments:

your fails column's length set low; need increase it.

fails int 1 fails int 10

plus, can use of present queries remove quotes in

where id='3' 

it's integer

where id=3 

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edit: added pdo example prepared statements; adjust suit.

<?php  $servername = "xxx"; // modify $username   = "xxx"; // these $password   = "xxx"; // $dbname     = "xxx"; // own  try {      $conn = new pdo("mysql:host=$servername;dbname=$dbname", $username, $password);     $conn->setattribute(pdo::attr_errmode, pdo::errmode_exception);      $query = 'update `your_table` set col = col + 1 id = :id';     $stmt = $conn->prepare( $query );     $stmt->execute(array(':id' => $userid));       } catch(pdoexception $e) {      echo "error: " . $e->getmessage(); } $conn = null;