mysql - how to check and rollback mySql queries

Question

I have a question about mySql queries which i use PHP to make -

In my code i insert data to table - main_query . if the insert part want well i do second insert query - sub_query.

How do i cancel the first insert query if the second was failed? I mean - is it possible to send both queries to be checked before i actually execute them? or - is it possible to do rollback for the first "main_query" query?

$main_query = "INSERT INTO table_1 (...) VALUES (...)";
$res = $conn->query($main_query);

if ($res)
{
    $id = mysqli_insert_id($conn);
    
    $sub_query = "INSERT INTO table_2 (...) VALUES (...)"; // use var "id" here
    $res = $conn->query($sub_query);
}

Answer 1

In this case you need to use transactions and rollback:

# start mysql transaction
mysqli_begin_transaction($conn, MYSQLI_TRANS_START_READ_WRITE);

$main_query = "INSERT INTO table_1 (...) VALUES (...)";
$res = mysqli_query($conn, $main_query);

if ($res)
{
    $id = mysqli_insert_id($conn);
    
    $sub_query = "INSERT INTO table_2 (...) VALUES (...)"; // use var "id" here
    $res = mysqli_query($conn, $sub_query);
    if ($res) {
        # both inserts succeed - do commit
        mysqli_commit($conn);
    }
    else {
        # second insert fail - do rollback
        mysqli_rollback($conn); 
    }
} else  {
    # first insert fail - do rollback
    mysqli_rollback($conn); 
}

or we can use object oriented style like:

# start mysql transaction
$mysqli->begin_transaction(MYSQLI_TRANS_START_READ_WRITE);

$main_query = "INSERT INTO table_1 (...) VALUES (...)";
$res = $mysqli->query($main_query);

if ($res)
{
    $id = $mysqli->insert_id;

    $sub_query = "INSERT INTO table_2 (...) VALUES (...)"; // use var "id" here
    $res = $mysqli->query($sub_query);
    if ($res) {
        # both inserts succeed - do commit
        $mysqli->commit();
    }
    else {
        # second insert fail - do rollback
        $mysqli->rollback(); 
    }
} else  {
    # first insert fail - do rollback
    $mysqli->rollback(); 
}

Look working example here PHPize.online