更新表格错误？ （SQLSTATE [HY000]：一般错误）

Question

I'm currently getting this error

[31-Aug-2018 15:50:46 America/New_York] PHP Fatal error:  Uncaught 

exception 'PDOException' with message 'SQLSTATE[HY000]: General error' 
in /home/crysuicn/public_html/products.php:22
Stack trace:
#0 /home/crysuicn/public_html/products.php(22): PDOStatement->fetch(2)
#1 {main}
  thrown in /home/crysuicn/public_html/products.php on line 22

Line 22 is:

while($row = $query->fetch(PDO::FETCH_ASSOC)){

Therefore the error would be somewhere in here, but I do not see what the error could be.

if(isset($_SESSION["discount"])){
        if($_SESSION["discount"] != "na"){
            $sql = "SELECT users FROM discounts WHERE name=:promo";
            $query = $st->prepare($sql);
            $query->execute(array(
                'promo' => $name
            ));
            if($query->rowCount()>0){
                while($row = $query->fetch(PDO::FETCH_ASSOC)){
                    if(!empty($row["users"])){
                        $usedips = $row["users"];
                        $usedips = $usedips.", ".$_SERVER["REMOTE_ADDR"];
                    }else{
                        $usedips = $_SERVER["REMOTE_ADDR"];
                    }
                    $sql = "UPDATE discounts SET users=:updatedips WHERE name=:name";
                    $query = $st->prepare($sql);
                    $query->execute(array(
                        'updatedips' => $usedips,
                        'name' => $name
                    ));
                }
            }
        }
    }
    $_SESSION["discount"] = "na";

Any help is much appreciated. I haven't had this error before so I am not sure where to go from here. It does go through and updates the table

Answer 1

You are destroying your $query handle by reusing it on the UPDATE query thus the while loop gets broken.

So use another variable for the statement handle used in the UPDATE.

Its also better to prepare a query once and reuse it many times, just replacing the variables. This allows the database to compile and optimise the query only once, but run it many times. It's quicker for your script and places less unnecessary load on the database.

if(isset($_SESSION["discount"])){
    if($_SESSION["discount"] != "na"){
        $sql = "SELECT users FROM discounts WHERE name=:promo";
        $query = $st->prepare($sql);
        $query->execute(array('promo' => $name));

        if($query->rowCount()>0){

            // prepare once use many times
            $sql = "UPDATE discounts 
                    SET users=:updatedips WHERE name=:name";   
            $stmt= $st->prepare($sql);

            while($row = $query->fetch(PDO::FETCH_ASSOC)){
                if(!empty($row["users"])){
                    $usedips = $row["users"];
                    $usedips = $usedips.", ".$_SERVER["REMOTE_ADDR"];
                }else{
                    $usedips = $_SERVER["REMOTE_ADDR"];
                }

                $stmt->execute(array('updatedips' => $usedips,'name' => $name));
            }
        }
    }
}
$_SESSION["discount"] = "na";

Answer 2

You're recycling variable names and sabotaging your loop. Rename the inner "query", or while you're at it, structure it differently:

        $select = $st->prepare("SELECT users FROM discounts WHERE name=:promo");
        $select->execute(array(
            'promo' => $name
        ));

        $update = $st->prepare("UPDATE discounts SET users=:updatedips WHERE name=:name");

        if ($select->rowCount() > 0) {
            while ($row = $select->fetch(PDO::FETCH_ASSOC)) {
                if(!empty($row["users"])){
                  $usedips = $row["users"];
                  $usedips = $usedips.", ".$_SERVER["REMOTE_ADDR"];
                } else {
                  $usedips = $_SERVER["REMOTE_ADDR"];
                }

                $update->execute(array(
                  'updatedips' => $usedips,
                  'name' => $name
                ));
            }
        }

Whenever possible give your variables meaningful, contextual names. $query is often too vague.

Plus use prepared statements effectively: Prepare once and execute many times if necessary.

It also looks like you're assembling a comma-separated value in a column which is a big problem for relational databases. Instead create a proper one-to-many relationship here. Try to avoid violating the Zero, One or Infinity Rule by understanding the idea behind proper database normalization .