1. Getting Crazy Creative
with WordPress Queries
Drew Jaynes
WordCamp Cape Town 2015

2. • Platform Engineer at 10up
• Docs Committer for WordPress core
• 4.2 Release Lead
• Developing with WordPress since 2009
• Slides: http://drewf.us/wcct
Hi, I’m Drew.

3. • Basics
• No-Nos
• Optimizations
• Creative Querying
Topics

4. Query Basics

5. The Loop
if ( have_posts() ) :
while ( have_posts() ) :
the_post();
...
endwhile;
endif;

6. The Loop: Internals
if ( $wp_query->have_posts() ) :
while ( $wp_query->have_posts() ) :
$wp_query->the_post();
...
endwhile;
endif;

7. WP_Query
// Query for the 7 latest, published posts.
$query = new WP_Query( array(
'posts_per_page' => 7,
'post_status' => 'publish'
) );

8. WP_Query: SQL
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts
WHERE 1=1
AND wp_posts.post_type = 'post'
AND wp_posts.post_status = 'publish'
ORDER BY wp_posts.post_date DESC
LIMIT 0, 7

9. • WP_Query wrapper
• Defaults: Filter suppression
• Defaults: No sticky posts
• Defaults: No found rows
• Array of results vs WP_Query instance
get_posts()

10. get_posts()
// Query for the 7 latest, published posts.
$query = get_posts( array(
'posts_per_page' => 7,
'post_status' => 'publish'
) );

11. get_posts(): SQL
SELECT wp_posts.ID FROM wp_posts
WHERE 1=1
AND wp_posts.post_type = 'post'
AND ( ( wp_posts.post_status = 'publish' ) )
ORDER BY wp_posts.post_date DESC
LIMIT 0, 7

12. • Action, not a filter
• Fires before the query actually runs
• Use query methods intead of top-level functio
e.g. $query->is_main_query()
pre_get_posts

13. pre_get_posts
/**
* Display both posts and pages in the home loop.
*
* @param WP_Query $query Main WP_Query instance.
*/
function pages_in_main_query( $query ) {
if ( ! is_admin() && is_home() ) {
$query->query_vars['post_type'] = array( 'post', 'page' );
}
}
add_action( 'pre_get_posts', 'pages_in_main_query' );

14. pre_get_posts: Original SQL
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts
WHERE 1=1
AND wp_posts.post_type = 'post'
AND (
wp_posts.post_status = ‘publish'
OR wp_posts.post_status = ‘private'
)
ORDER BY wp_posts.post_date DESC
LIMIT 0, 10

15. pre_get_posts: SQL
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts
WHERE 1=1
AND wp_posts.post_type IN ( 'post', 'page' )
AND (
wp_posts.post_status = ‘publish'
OR wp_posts.post_status = ‘private'
)
ORDER BY wp_posts.post_date DESC
LIMIT 0, 10

16. No-Nos

17. • Completely overrides the main query
• Very few valid use cases
• Custom page template archives
query_posts()

18. query_posts()
query_posts( array(
'post_type' => ‘page’,
‘post_per_page' => 4
) );

19. posts_per_page
get_posts( array(
‘posts_per_page’ => -1,
‘posts_per_page’ => 100
) );

20. Optimization

21. • update_post_term_cache
• update_post_meta_cache
• no_found_rows
• fields
• posts_per_page
Optimizing WP_Query

22. Optimizing WP_Query
$query = new WP_Query( array(
'update_post_term_cache' => false,
'update_post_meta_cache' => false,
'posts_per_page' => 100,
'no_found_rows' => true,
'fields' => 'ids'
) );

23. Creative Querying

24. WP_Query

25. • posts_* filters
• pre_get_posts action
WP_Query hooks

26. WP_Query orderby
$posts = get_posts( array(
'posts_per_page' => 15,
'orderby' => array(
'post_date' => 'DESC',
'post_title' => 'ASC'
),
) );

27. WP_Query orderby: SQL
SELECT wp_posts.ID FROM wp_posts
WHERE 1=1
AND wp_posts.post_type = 'post'
AND ( ( wp_posts.post_status = 'publish' ) )
ORDER BY wp_posts.post_date DESC, wp_posts.post_title ASC
LIMIT 0, 15

28. • Available 4.2+
• Order by independent meta clauses
• WP_Meta_Query, WP_User_Query,
WP_Comment_Query
WP_Query orderby: meta clauses

29. WP_Query orderby: meta clauses
$posts = get_posts( array(
'meta_query' => array(
'relation' => 'AND',
'state_clause' => array(
'key' => 'state',
'value' => 'Colorado'
),
'city_clause' => array(
'key' => 'city',
'compare' => 'EXISTS'
)
),
'orderby' => array(
'state_clause' => 'ASC',
'city_clause' => 'DESC'
)
) );

30. WP_Query orderby: meta clauses
$posts = get_posts( array(
'meta_query' => array(
'relation' => 'AND',
'state_clause' => array(
'key' => 'state',
'value' => 'Colorado'
),
'city_clause' => array(
'key' => 'city',
'compare' => 'EXISTS'
)
),
'orderby' => array(
'state_clause' => 'ASC',
'city_clause' => 'DESC'
)
) );

31. WP_Query orderby: SQL
SELECT wp_posts.ID FROM wp_posts
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 )
WHERE 1=1
AND (
( wp_postmeta.meta_key = ‘state’
AND CAST( wp_postmeta.meta_value AS CHAR ) = ‘Colorado'
)
AND mt1.meta_key = ‘city'
)
AND wp_posts.post_type = 'post'
AND ( ( wp_posts.post_status = 'publish' ) )
GROUP BY wp_posts.ID
ORDER BY
CAST( mt1.meta_value AS CHAR ) ASC,
CAST( wp_postmeta.meta_value AS CHAR ) DESC
LIMIT 0, 5

32. WP_User_Query

33. WP_User_Query
// Query for users registered on a Tuesday.
$query = new WP_User_Query( array(
'date_query' => array(
array(
'column' => 'user_registered',
'dayofweek' => 3 // Tuesday
)
),
) );

34. Custom WP_Query Orderby

35. • Order results by a value in a custom table
• Adds an additional LEFT JOIN
WP_Query orderby with custom tables

36. Joining Custom Tables: JOIN
/**
* Join vote totals table to the 'books' custom post type query.
*
* @param string $join JOIN query clauses.
* @param WP_Query $query Current WP_Query instance.
* @return string The filtered JOIN clauses.
*/
function join_votes_table( $join, $query ) {
global $wpdb;
if ( ! is_admin() ) {
if ( isset( $query->query_vars['post_type'] )
&& 'books' == $query->query_vars[‘post_type']
) {
$votes = $wpdb->prefix . 'up_down_post_vote_totals';
$join .= "LEFT JOIN $votes ON $wpdb->posts.ID = $votes.post_id ";
}
}
return $join;
}
add_filter( 'posts_join', 'join_votes_table', 10, 2 );

37. Joining Custom Tables: ORDERBY
/**
* Order by vote totals descending, then post date descending.
*
* @param string $orderby ORDER BY query clauses.
* @param WP_Query $query Current WP_Query instance.
* @return string The filtered ORDER BY query clauses.
*/
function orderby_votes_and_date( $orderby, $query ) {
global $wpdb;
if ( ! is_admin() ) {
if ( isset( $query->query_vars['post_type'] )
&& 'books' == $query->query_vars[‘post_type']
) {
$votes = $wpdb->prefix . 'up_down_post_vote_totals';
$orderby = "$votes.vote_count_up DESC, $wpdb->posts.post_date DESC";
}
}
return $orderby;
}
add_filter( 'posts_orderby', 'orderby_votes_and_date', 10, 2 );

38. Joining Custom Tables: SQL
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts
WHERE 1=1
AND wp_posts.post_type = 'books'
AND ( wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private' )
ORDER BY wp_posts.post_date DESC
LIMIT 0, 10
Original SQL:

39. Joining Custom Tables: SQL
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts
LEFT JOIN wp_up_down_post_vote_totals
ON wp_posts.ID = wp_up_down_post_vote_totals.post_id
WHERE 1=1
AND wp_posts.post_type = 'books'
AND ( wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private' )
ORDER BY
wp_up_down_post_vote_totals.vote_count_up DESC,
wp_posts.post_date DESC
LIMIT 0, 10
SQL with the JOIN:

40. • WordPress Code Reference
• WP_Query Reference (Codex)
• Trunk wp-includes/
Resources

41. Questions?
Drew Jaynes | @DrewAPicture
Slides: http://drewf.us/wcct