What is the purpose of using auto increment in PHP and what potential issues can arise when using multiple auto increment fields?

When using multiple auto increment fields in PHP, the potential issue that can arise is that each table can only have one auto increment field. To solve this issue, you can manually generate unique IDs for the other fields using a combination of timestamp and a random number.

// Generate a unique ID for a field
$unique_id = time() . mt_rand(1000, 9999);