Why Do My PHP MySQL Inserts Fail Inconsistently When Handling Single Quotes?

Escaping Single Quotes in PHP MySQL Inserts: A Deeper Dive into Query Execution

While inserting data into a MySQL database, it's crucial to ensure the correct handling of single quotes ('). However, sometimes developers encounter an inexplicable situation where a query fails due to a single quote in the second insert, while the first one succeeds seamlessly.

In these scenarios, it's essential to understand the potential reasons for this inconsistent behavior. Although the information entered in forms is often represented as strings, it's important to consider the following:

Query Execution and Magic Quotes

• Query 1: This query works without escaping the single quote because the magic_quotes_gpc PHP setting is turned on. This setting automatically escapes strings obtained from form inputs ($_GET, $_POST, $_COOKIES).
• Query 2: When magic_quotes_gpc is enabled, the stored data remains unescaped, making it susceptible to conflicts with single quotes. Hence, the query fails with mysql_error() when a single quote is encountered.

Escaping with mysql_real_escape_string()

The solution lies in using the mysql_real_escape_string() function to appropriately escape all strings regardless of the magic_quotes_gpc setting. This function prepares strings for insertion into MySQL, preventing malicious characters from interfering with the database. By incorporating this function in both of the queries, the inconsistencies can be resolved:

$result = mysql_query("INSERT INTO job_log
(order_id, supplier_id, category_id, service_id, qty_ordered, customer_id, user_id, salesperson_ref, booking_ref, booking_name, address, suburb, postcode, state_id, region_id, email, phone, phone2, mobile, delivery_date, stock_taken, special_instructions, cost_price, cost_price_gst, sell_price, sell_price_gst, ext_sell_price, retail_customer, created, modified, log_status_id)
VALUES
('$order_id', '$supplier_id', '$category_id', '{$value['id']}', '{$value['qty']}', '$customer_id', '$user_id', '$salesperson_ref', '$booking_ref', '$booking_name', '$address', '$suburb', '$postcode', '$state_id', '$region_id', '" . mysql_real_escape_string($email) . "', '" . mysql_real_escape_string($phone) . "', '" . mysql_real_escape_string($phone2) . "', '" . mysql_real_escape_string($mobile) . "', STR_TO_DATE('$delivery_date', '%d/%m/%Y'), '$stock_taken', '" . mysql_real_escape_string($special_instructions) . "', '$cost_price', '$cost_price_gst', '$sell_price', '$sell_price_gst', '$ext_sell_price', '$retail_customer', '".date('Y-m-d H:i:s', time())."', '".date('Y-m-d H:i:s', time())."', '1')");

$query = mysql_query("INSERT INTO message_log
(order_id, timestamp, message_type, email_from, supplier_id, primary_contact, secondary_contact, subject, message_content, status)
VALUES
('$order_id', '".date('Y-m-d H:i:s', time())."', '$email', '$from', '$row->supplier_id', '" . mysql_real_escape_string($row->primary_email) . "', '" . mysql_real_escape_string($row->secondary_email) . "', '" . mysql_real_escape_string($subject) . "', '" . mysql_real_escape_string($message_content) . "', '1')");

With this modification, both queries will operate correctly even when encountering single quotes in the data, ensuring consistent database interactions.

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