Using WordPress ‘like_escape()’ PHP function
Formerly used to escape strings before searching the DB. It was poorly documented and never worked as described.
WordPress
Using WordPress ‘is_main_site()’ PHP function
Determines whether a site is the main site of the current network.
Using WordPress ‘is_login()’ PHP function
Determines whether the current request is for the login screen.
Using WordPress ‘iso8601_to_datetime()’ PHP function
Given an ISO 8601 (Ymd H:i:sO) date, returns a MySQL DateTime (Y-m-d H:i:s) format used by post_date[_gmt].