MySQL中的PHP更新数据不一致，有时仅更新

Question

I have values which use the GET method to send URL variables to a PHP page using Ajax.

On the page, I have:

$value=$_GET["q"];
$id=$_GET["id"];
$mod=$_GET["mod"];

I started out using the UPDATE SET method to modify values in a mySQL database.

I used: $num_rows= mysql_num_rows($result);

With an If Else statement to either Insert the values (if not there) or Update the column "Attribute"

But this was very inconsistant and often would not UPDATE, and there developed several duplicate values (even though if($num_rows > 0){ (WHERE Object_ID = '".$mod."' AND Type='".$id."') it SHOULD NOT have inserted, but it did.)

So I switched to this:

$sql="SELECT * FROM Attributes WHERE Object_ID = '".$mod."' AND Type='".$id."'";
$result = mysql_query($sql);

    mysql_query("DELETE FROM Attributes WHERE Object_ID = '".$mod."' AND Type = '".$id."'");

    mysql_query("INSERT INTO Attributes (Object_ID, Type, Attribute)
        VALUES ('".$mod."', '".$id."', '".$value."')");

I know, really bad idea. But Even this method doesn't always insert the values correctly.

I know that the variables are getting to the page, because the response would be written in a div using innerHTML, and it always showed up correctly.

How can I ensure that the values are ALWAYS updated/inserted in the database?

Answer 1

为什么不为条件运行SELECT COUNT（*）并检查返回的内容以及基于该条件运行UPDATE或INSERT的原因？

Answer 2

i am really confused what is wrong with your database operation but the only way to ensure is to send back response from your php script to ajax. It can be json or simple text informing you that which action was requested and what is performed. Depending on the response you can adjust what you want.

Answer 3

You have to query the table to find out if the id already exists there or not if it exits then write an Update Query ie

 $update = "update tbl_name set column=value where id = $_GET['id']"

and if the id does not exist then use the insert

$insert = "Insert into ......"

hope this solves your issue. And Further more you have to echo out the response here in either a string format or a some other value which you will get in the success method of $.Ajax.

Answer 4

No need to query the database to see if the data exists already. As long as you have good data, you can delete the row every time. If the row doesn't exist, the DELETE does nothing.

Run these two queries every time, and you will be fine.

mysql_query("DELETE FROM Attributes WHERE Object_ID = '$mod' AND Type='$id'"); 
mysql_query("INSERT INTO Attributes (Object_ID, Type, Attribute) VALUES ('$mod', '$id', '$value'");

And please at a minimum, before you do anything with $_GET, run those through mysql_real_escape_string first. You should probably be doing more checking just to make sure that the values passed in are valid.

$value=mysql_real_escape_string($_GET["q"]); 
$id=mysql_real_escape_string($_GET["id"]); 
$mod=mysql_real_escape_string($_GET["mod"]);