Stop duplicate messages from appearing in AJAX chat feature (JavaScript, PHP, MySQL)

I developed a real-time chat system using AJAX, Javascript, PHP, and MySQL.

Chat data is sent via JSON from a PHP page that retrieves information from a MySQL database. Each message is stored in an array and fetched through an AJAX call at regular intervals. The timestamp of each message post is included in the database as well (including milliseconds such as 1288147058.77943).

With every AJAX request, I update a column in the user database with the timestamp indicating when the chat data was last accessed. To prevent duplicate messages from appearing, I use a query like this to retrieve only new messages since the last check:

SELECT user, message FROM chat WHERE posted_time >= '$last_check_get'

Occasionally, due to rapid successive requests, the same messages may be displayed twice even though they were not posted again. What strategies can I employ to address this issue?

phpmysqlajaxchat

Answer №1

Try giving each message a unique serial number instead of using time-stamps. The process for checking new messages will stay unchanged.

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