Retrieve row from database every set seconds

I'm working on a project in Codeigniter . I have a challenge of pulling rows from a particular table in my database,say user_table every 20 seconds.

Here's what I want to achieve. Let's say I have 15 rows in my user_table, I want to pop up each row every 20 seconds at the header of my home page and make the loop start over when it gets to the last row. Please how do I achieve this in Codeigniter?...I'm using Codeigniter 3 for the project.

I'll gladly appreciate any assistance I get....Thank you