MySQL仅在行之前已插入的情况下更新

Question

I want to only run the update query if row exists (and was inserted). I tried several different things but this could be a problem with how I am looping this. The insert which works ok and creates the record and the update should take the existing value and add it each time (10 exists + 15 added, 25 exists + 15 added, 40 exists... I tried this in the loop but it ran for every item in a list and was a huge number each time. Also the page is run each time when a link is clicked so user exits and comes back

while($store = $SQL->fetch_array($res_sh)) 
{
$pm_row = $SQL->query("SELECT * FROM `wishlist` WHERE shopping_id='".$store['id']."'");
$myprice = $store['shprice'];
    $sql1 =  "insert into posted (uid,price) Select '$uid','$myprice'
        FROM posted WHERE NOT EXISTS (select * from `posted` WHERE `uid` = '$namearray[id]') LIMIT 1";
    $query = mysqli_query($connection,$sql1);  
}

$sql2 = "UPDATE posted SET `price` = price + '$myprice', WHERE shopping_id='".$_GET['id']."'"; 
$query = mysqli_query($connection,$sql2);

Answer 1

Utilizing mysqli_affected_rows on the insert query, verifying that it managed to insert, you can create a conditional for the update query.

However, if you're running an update immediately after an insert, one is led to believe it could be accomplished in the same go. In this case, with no context, you could just multiply $myprice by 2 before inserting - you may look into if you can avoid doing this.

Additionally, but somewhat more complex, you could utilize SQL Transactions for this, and make sure you are exactly referencing the row you would want to update. If the insert failed, your update would not happen.

Granted, if you referenced the inserted row perfectly for your update then the update will not happen anyway. For example, having a primary, auto-increment key on these rows, use mysqli_insert_id to get the last inserted ID, and updating the row with that ID. But then this methodology can break in a high volume system, or just a random race event, which leads us right back to single queries or transaction utilization.