WP_Query offset argument does not work

Question

I want to display all posts starting from a certain offset, my query is:

WP_Query( array(
    'posts_per_page'    => -1,
    'offset'            => 20,
    'cat'               => 5,
) );

This query shows all posts without starting from the offset value. Whys is that?

Answer 1

The offset index for WP_Query generally works with pagination. When you set pagination to a -1 the function assumes you're getting all posts and there will be no pagination or offset. So to counteract this you would set the posts_per_page to a high number like 999. Reading the Function Reference on WP_Query the pagination section says:

'posts_per_page'=>-1 to show all posts (the 'offset' parameter is ignored with a -1 value). Set the ‘paged’ parameter if pagination is off after using this parameter.