WordPress at a glance
filter is not described

posts_join_request filter-hook . WP 2.5.0

Filters the JOIN clause of the query.

For use by caching plugins.

Usage

add_filter( 'posts_join_request', 'filter_function_name_8107', 10, 2 );
function filter_function_name_8107( $join, $this ){
	// filter...

	return $join;
}
$join(string)
The JOIN clause of the query.
$this(WP_Query)
The WP_Query instance (passed by reference).

Where the hook is called

WP_Query::get_posts()
posts_join_request
wp-includes/class-wp-query.php 2643
$join = apply_filters_ref_array( 'posts_join_request', array( $join, &$this ) );

Where the hook is used (in WP core)

Does not used.