Question

I have a php file which performs a series of insert queries. If any of the queries generates an error, I would like to return the error message and query string and roll back all the queries

So far I have this:

mysql_query("SET autocommit=0;");
mysql_query("BEGIN;");
$sql ="SOME MALFORMED QUERY";

mysql_query($sql);

if(mysql_error()){
    mysql_query("rollback;");
    $arr = array("returnCode" => 0, "returnMessage" => "Query failed: " .$sql. mysql_error());
    echo json_encode($arr);
    die();
}

However, In javascript all I’m seeing returned in the return message JSON field is ‘Query failed: ‘. Any idea why this is?

Answer 1

The problem is with your ROLLBACK query: as explained in the manual, mysql_error returns the error text from the last MySQL function. Since you used mysql_query again, the previous error is lost.

I suggest this code:

mysql_query("SET autocommit=0;");
mysql_query("BEGIN;");
$sql ="SOME MALFORMED QUERY";

mysql_query($sql);
$error = mysql_error();
if($error){
    mysql_query("rollback;");
    $arr = array("returnCode" => 0, "returnMessage" => "Query failed: $sql, Error: $error");
    echo json_encode($arr);
    die();
}

Executing ROLLBACK in case an error occurs seems useless. The manual explains:
Rolling back can be a slow operation that may occur implicitly without the user having explicitly asked for it (for example, when an error occurs)

The following code should then be enough:

mysql_query("SET autocommit=0;");
mysql_query("BEGIN;");
$sql ="SOME MALFORMED QUERY";

mysql_query($sql);
if(mysql_error()){
    $arr = array("returnCode" => 0, "returnMessage" => "Query failed: $sql, Error: ".mysql_error());
    echo json_encode($arr);
    die();
}