Question

I have 2 sql queries to execute, but I want it to execute all or if error in one query then dont execute any. I’m using php. I used to use try and catch in .NET but I’m new to php.

Below is the code which i was trying to do:

function Registration($UserFirstname,$UserLastname){
$sql="INSERT INTO table1 (fieldname1,fieldname2) VALUES ('$UserFirstname','$UserLastname')";
$res=mysql_query($sql) or die(mysql_error());
$sql="INSERT INTO table2 (fieldname1,fieldname2) VALUES ('$UserFirstname','$UserLastname')";
$res=mysql_query($sql) or die(mysql_error());}

Answer 1

The problem you’re probably facing with try...catch is that PHP has two different error handling mechanisms: error reporting and exceptions. You cannot catch exceptions unless the underlying code throws them and good old mysql_query() will trigger warnings rather than throwing exceptions. There’re several workarounds but, if you are interested in writing good object-oriented code, I suggest you switch to PDO.

In any case, if you want to stick to good old MySQL library, your code should basically work:

$res=mysql_query($sql) or die(mysql_error());

The explanation:

• mysql_query() returns FALSE if the query fails (e.g., you get a duplicate key)
• The right side of the or expression will only execute if the left side is FALSE
• die() aborts the script, thus preventing the next queries to be executed

However, I presume that you don’t want to abort in the middle of nowhere. If we add some missing bits (such as proper SQL generation and code indentation) we get this:

function Registration($UserFirstname,$UserLastname){
    $sql = sprintf("INSERT INTO table1 (fieldname1,fieldname2) VALUES ('%s','%s')";
        mysql_real_escape_string($UserFirstname),
        mysql_real_escape_string($UserLastname)
    );
    $res = mysql_query($sql);
    if( !$res ){
        return FALSE;
    }


    $sql = sprintf("INSERT INTO table2 (fieldname1,fieldname2) VALUES ('%s','%s')";
        mysql_real_escape_string($UserFirstname),
        mysql_real_escape_string($UserLastname)
    );
    $res = mysql_query($sql);
    if( !$res ){
        return FALSE;
    }


    return TRUE;
}

About transactions

Please note that you still need to use transactions if there’s a chance that the second query fails. Transactions are not particularly difficult to use, the only requirements are:

1. Define the involved tables as InnoDB
2. Run a START TRANSACTION query on top of the function
3. Run a COMMIT query at the end of the function