Wordpress meta_query

Question

I'm struggling with a wp_query and i need your help.

I have 3 custom fields called "Agenda_day", "Agenda_month", "Agenda_year", representing the day, month and year of an event.

I want to order the results of my query by day, then month, and finally year, ascendingly.

Here is my query :

$query_agenda = new WP_Query(
    array(
        'posts_per_page' => 8, 
        'cat' => 4, 
        'meta_query' => 
            array(
                'relation' => 'AND', 
                'day' => array('key' => 'Agenda_day', 'compare' => 'EXISTS'), 
                'month' => array('key' => 'Agenda_month', 'compare' => 'EXISTS'), 
                'year' => array('key' => 'Agenda_year', 'compare' => 'EXISTS')
            ), 
        'orderby' => array('day' => 'ASC', 'month' => 'ASC', 'year' => 'ASC')
    )
);

And this does not work ... can you explain me why and show me how to fix it ?

Thank you !

EDIT

Here is the executed query (results are returned but not well ordered)

SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts LEFT JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id) INNER JOIN wp_postmeta ON ( wp_posts.ID = wp_postmeta.post_id ) INNER JOIN wp_postmeta AS mt1 ON ( wp_posts.ID = mt1.post_id ) INNER JOIN wp_postmeta AS mt2 ON ( wp_posts.ID = mt2.post_id ) WHERE 1=1 AND ( wp_term_relationships.term_taxonomy_id IN (4) ) AND ( wp_postmeta.meta_key = 'Agenda_jour' AND mt1.meta_key = 'Agenda_mois' AND mt2.meta_key = 'Agenda_annee' ) AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') GROUP BY wp_posts.ID ORDER BY CAST(wp_postmeta.meta_value AS CHAR) ASC, CAST(mt1.meta_value AS CHAR) ASC, CAST(mt2.meta_value AS CHAR) ASC LIMIT 0, 8

Answer 1

Problem solved !

• i was dealing with different formats in the custom fields : some days and months were on 1 character ("6") and others on two ("06"), so the system couldn't sort it well

• second point is, as i'm dealing with dates, i have to reorder the "orderby" instruction from "day, month, year" to "year, month, day"

Answer 2

https://codex.wordpress.org/Class_Reference/WP_Query https://codex.wordpress.org/Class_Reference/WP_Meta_Query

please check above both links you will get your answer and your orderby arguments which you are passing it's wrong