This is an update to a talk I gave three years ago at WordCamp Cape Town 2015. We’re at a point now where we have these incredibly powerful query classes in WordPress core that allow you to really tailor down to whatever criterion you want. In this talk, I take you through the outermost abstraction layers and deep into the SQL that WordPress actually uses to query for stuff on your site – it’s very much a “sky’s the limit” kind of situation. Queries are really interesting and powerful, and a lot of people are intimidated by advanced queries, even with the abstraction layers that WordPress has put in place.

1. Getting Creative
with WordPress Queries
Drew Jaynes
WordCamp Portland 2018

2. • Chief Bottle Washer
at Sandhills Brewing Development
• WordPress Core Developer
• @DrewAPicture all the places
Drew Jaynes

3. Slides
http://drewf.us/wcpdx18

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

5. • Lots of code
• Lots of SQL
• No display
Expectations

6. Query Basics

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

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

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

10. 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

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

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

13. 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

14. 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

15. • Action, not a filter
• $wp_query passed by reference
• Fires before the query actually runs
• Use query methods like $query->is_main_query()
• is_main_query() === _doing_it_wrong()
pre_get_posts

16. 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' );

17. 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'
)
ORDER BY wp_posts.post_date DESC
LIMIT 0, 10

18. pre_get_posts: New 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'
)
ORDER BY wp_posts.post_date DESC
LIMIT 0, 10

19. No-Nos

20. • Completely overrides the main query
• Very few valid use cases
• Can break pagination (and other stuff)
• wp_reset_query()
• Don’t use it
query_posts()

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

22. Optimization

23. • update_post_term_cache (+1 query)
• update_post_meta_cache (+1 query)
• no_found_rows (+1 query)
• fields
• posts_per_page
Optimizing WP_Query

24. posts_per_page: Unbounded
get_posts( array(
‘posts_per_page’ => -1,
‘posts_per_page’ => 100
) );

25. 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'
) );

26. Optimize carefully

27. Creative Querying

28. WP_Query

29. • posts_* filters
• pre_get_posts action
WP_Query hooks

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

31. WP_Query multiple 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

32. • Order by independent, named meta clauses
• WP_Meta_Query, WP_User_Query,
WP_Comment_Query
WP_Query orderby: meta clauses

33. 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'
)
) );

34. 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

35. WP_User_Query

36. WP_User_Query registered on Tuesday
// Query for users registered on a Tuesday.
$query = new WP_User_Query( array(
‘count_total' => false,
‘orderby' => ‘display_name’,
'date_query' => array(
array(
'column' => 'user_registered',
'dayofweek' => 3 // Tuesday
)
),
) );

37. WP_User_Query registered on Tuesday: SQL
SELECT wp_users.*.ID FROM wp_users
WHERE 1=1
AND (
DAYOFWEEK( wp_users.user_registered ) = 3
)
ORDER BY
display_name ASC

38. WP_User_Query lifetime value
// Query for top 10 customers with a lifetime value 1,000+
$query = new WP_User_Query( array(
‘number’ => 10,
‘count_total’ => false, // No pagination.
‘meta_query’ => array(
‘lifetime_value’ => array(
‘key’ => ‘lifetime_value’,
‘compare’ => ‘>=’,
‘value’ => 1000,
‘type’ => ‘DECIMAL’,
),
),
// Order by lifetime value high to low, then name A-Z
'orderby' => array(
‘lifetime_value’ => ‘DESC’,
‘name’ => ‘ASC’,
) );

39. WP_User_Query lifetime value: SQL
SELECT wp_users.*.ID FROM wp_users
INNER JOIN wp_usermeta ON ( wp_users.ID = wp_usermeta.user_id )
WHERE 1=1
AND (
wp_usermeta.meta_key = ‘lifetime_value’
AND CAST( wp_usermeta.meta_value AS DECIMAL >= ‘1000’ )
ORDER BY
CAST( wp_usermeta.meta_value AS DECIMAL ) DESC,
display_name ASC
LIMIT 0, 10

40. WP_Term_Query

41. WP_Term_Query name__like
$query = new WP_Term_Query( array(
'taxonomy' => ‘mascots’,
‘name__like’ => ‘monster’,
‘number’. => 6,
‘order’. => ‘ASC’,
'orderby' => ‘name’,
'fields' => ‘names’,
‘hide_empty' => false,
) );

42. WP_Term_Query name__like: SQL
SELECT t.name FROM wp_terms AS t
INNER JOIN wp_term_taxonomy AS tt ON t.term_id = tt.term_id
WHERE
tt.taxonomy IN (‘mascots’) AND t.name LIKE ‘%monster%'
ORDER BY t.name ASC
LIMIT 6

43. WP_Query: Custom Orderby

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

45. 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 );

46. 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 );

47. Joining Custom Tables: Original 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

48. Joining Custom Tables: SQL with JOIN
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

49. • Debug Bar
• WordPress Developer Hub
• WP_Query (Code Reference)
• Trunk wp-includes/
Plugins & Resources

50. Questions?
Drew Jaynes | @DrewAPicture
Slides: http://drewf.us/wcpdx18