[php] PHP + MySQL transactions examples

I really haven't found normal example of PHP file where MySQL transactions are being used. Can you show me simple example of that?

And one more question. I've already done a lot of programming and didn't use transactions. Can I put a PHP function or something in header.php that if one mysql_query fails, then the others fail too?

I think I have figured it out, is it right?:

mysql_query("SET AUTOCOMMIT=0");
mysql_query("START TRANSACTION");

$a1 = mysql_query("INSERT INTO rarara (l_id) VALUES('1')");
$a2 = mysql_query("INSERT INTO rarara (l_id) VALUES('2')");

if ($a1 and $a2) {
    mysql_query("COMMIT");
} else {        
    mysql_query("ROLLBACK");
}

One more procedural style example with mysqli_multi_query, assumes $query is filled with semicolon-separated statements.

mysqli_begin_transaction ($link);

for (mysqli_multi_query ($link, $query);
    mysqli_more_results ($link);
    mysqli_next_result ($link) );

! mysqli_errno ($link) ?
    mysqli_commit ($link) : mysqli_rollback ($link);

As this is the first result on google for "php mysql transaction", I thought I'd add an answer that explicitly demonstrates how to do this with mysqli (as the original author wanted examples). Here's a simplified example of transactions with PHP/mysqli:

// let's pretend that a user wants to create a new "group". we will do so
// while at the same time creating a "membership" for the group which
// consists solely of the user themselves (at first). accordingly, the group
// and membership records should be created together, or not at all.
// this sounds like a job for: TRANSACTIONS! (*cue music*)

$group_name = "The Thursday Thumpers";
$member_name = "EleventyOne";
$conn = new mysqli($db_host,$db_user,$db_passwd,$db_name); // error-check this

// note: this is meant for InnoDB tables. won't work with MyISAM tables.

try {

    $conn->autocommit(FALSE); // i.e., start transaction

    // assume that the TABLE groups has an auto_increment id field
    $query = "INSERT INTO groups (name) ";
    $query .= "VALUES ('$group_name')";
    $result = $conn->query($query);
    if ( !$result ) {
        $result->free();
        throw new Exception($conn->error);
    }

    $group_id = $conn->insert_id; // last auto_inc id from *this* connection

    $query = "INSERT INTO group_membership (group_id,name) ";
    $query .= "VALUES ('$group_id','$member_name')";
    $result = $conn->query($query);
    if ( !$result ) {
        $result->free();
        throw new Exception($conn->error);
    }

    // our SQL queries have been successful. commit them
    // and go back to non-transaction mode.

    $conn->commit();
    $conn->autocommit(TRUE); // i.e., end transaction
}
catch ( Exception $e ) {

    // before rolling back the transaction, you'd want
    // to make sure that the exception was db-related
    $conn->rollback(); 
    $conn->autocommit(TRUE); // i.e., end transaction   
}

Also, keep in mind that PHP 5.5 has a new method mysqli::begin_transaction. However, this has not been documented yet by the PHP team, and I'm still stuck in PHP 5.3, so I can't comment on it.

<?php

// trans.php
function begin(){
    mysql_query("BEGIN");
}

function commit(){
    mysql_query("COMMIT");
}

function rollback(){
    mysql_query("ROLLBACK");
}

mysql_connect("localhost","Dude1", "SuperSecret") or die(mysql_error());

mysql_select_db("bedrock") or die(mysql_error());

$query = "INSERT INTO employee (ssn,name,phone) values ('123-45-6789','Matt','1-800-555-1212')";

begin(); // transaction begins

$result = mysql_query($query);

if(!$result){
    rollback(); // transaction rolls back
    echo "transaction rolled back";
    exit;
}else{
    commit(); // transaction is committed
    echo "Database transaction was successful";
}

?>

Please check which storage engine you are using. If it is MyISAM, then Transaction('COMMIT','ROLLBACK') will not be supported because only the InnoDB storage engine, not MyISAM, supports transactions.

I think I have figured it out, is it right?:

mysql_query("START TRANSACTION");

$a1 = mysql_query("INSERT INTO rarara (l_id) VALUES('1')");
$a2 = mysql_query("INSERT INTO rarara (l_id) VALUES('2')");

if ($a1 and $a2) {
    mysql_query("COMMIT");
} else {        
    mysql_query("ROLLBACK");
}

When using PDO connection:

$pdo = new PDO('mysql:host=localhost;dbname=mydb;charset=utf8', $user, $pass, [
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION, // this is important
]);

I often use the following code for transaction management:

function transaction(Closure $callback)
{
    global $pdo; // let's assume our PDO connection is in a global var

    // start the transaction outside of the try block, because
    // you don't want to rollback a transaction that failed to start
    $pdo->beginTransaction(); 
    try
    {
        $callback();
        $pdo->commit(); 
    }
    catch (Exception $e) // it's better to replace this with Throwable on PHP 7+
    {
        $pdo->rollBack();
        throw $e; // we still have to complain about the exception
    }
}

Usage example:

transaction(function()
{
    global $pdo;

    $pdo->query('first query');
    $pdo->query('second query');
    $pdo->query('third query');
});

This way the transaction-management code is not duplicated across the project. Which is a good thing, because, judging from other PDO-ralated answers in this thread, it's easy to make mistakes in it. The most common ones being forgetting to rethrow the exception and starting the transaction inside the try block.

I had this, but not sure if this is correct. Could try this out also.

mysql_query("START TRANSACTION");
$flag = true;
$query = "INSERT INTO testing (myid) VALUES ('test')";

$query2 = "INSERT INTO testing2 (myid2) VALUES ('test2')";

$result = mysql_query($query) or trigger_error(mysql_error(), E_USER_ERROR);
if (!$result) {
$flag = false;
}

$result = mysql_query($query2) or trigger_error(mysql_error(), E_USER_ERROR);
if (!$result) {
$flag = false;
}

if ($flag) {
mysql_query("COMMIT");
} else {        
mysql_query("ROLLBACK");
}

Idea from here: http://www.phpknowhow.com/mysql/transactions/

I made a function to get a vector of queries and do a transaction, maybe someone will find out it useful:

function transaction ($con, $Q){
        mysqli_query($con, "START TRANSACTION");

        for ($i = 0; $i < count ($Q); $i++){
            if (!mysqli_query ($con, $Q[$i])){
                echo 'Error! Info: <' . mysqli_error ($con) . '> Query: <' . $Q[$i] . '>';
                break;
            }   
        }

        if ($i == count ($Q)){
            mysqli_query($con, "COMMIT");
            return 1;
        }
        else {
            mysqli_query($con, "ROLLBACK");
            return 0;
        }
    }