How to determine if a MySQL update query succeeded when the data passed in the query is the same as what is already in the database?

Let's say you have a form with pre-populated data from your database, and you allow your users to make changes and save the form. If the user clicks the save button without making any changes, 开发者_Go百科MySQL will not actually perform a write operation, and therefore the affected_rows will return 0.

I understand the behavior, but what is the best practice for determining if an update failed, other than checking for the number of affected_rows?

What is the best practice for differentiating between an update that actually failed, and one that "succeeded" but resulted in 0 affected_rows so that I can provide feedback to the user?

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Just check if no errors occurred after execution of query.
If you use mysql, check mysql_error():
if (!mysql_error()) print 'all is fine';
Same for mysqli.

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Variation 1:

mysql_query() or die('error');

Variation 2:

$conn = mysql_query();
if(!$conn) {//Error code here}

Variation 3:

try {
  $conn = mysql_query();
  if (!$conn) throw new Exception("mysql Error");
} catch(Exception $e) {
  echo $e->getMessage();
}

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[affected_rows()][1] is -1 if a query fails, not zero.

[1]: http://www.php.net/manual/en/function.mysql-affected-rows.php

It may return 0 if no changes were made to the row (same values), or if mysql didnt find a row to update. It will only return -1 due syntax erro

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if the update "fails" due to syntax error, or other mysql will return an error code on the actual mysql query and affected_rows will return with yet another error.

Php for example:

$qry = mysql_query("update blah where IamaSyntaxerror,33");
if ($qry === FALSE) { echo "an error has occured"; }

else  { mysql_affected_rows() == 0  means no updates occured