Allow to specify when SQL queries should not be cached

[sirzooro]

Most of SELECT queries executed by WP core or plugins can be safely cached by plugins like ​DB Cache Reloaded. However there are some which are different every time (e.g. includes current date and time in WHERE clause), return different records every time (e.g. use RAND()), etc. Therefore I suggest to add common way to tell which queries should not be cached.

Attached patch adds new parameter $maybe_cache to all functions of wpdb class, which can be used to execute SELECT query.

2nd patch changes get_calendar() to use this new parameter - it executes two queries with current date/time in WHERE clause.

[Denis-de-Bernardy]

suggesting close as wontfix. why not simply check for rand() in the query string?

[ryan]

Agreed.