Wordpress include post associated to specific term in search results - mysql

Question

I'm working on a custom search engine for my WordPress site. The DB for the project is pretty big ( 300k+ posts ) so performance is key.
I have a searchbar returning posts ('clients' & 'professionnels') and i'm trying to limit search results to post title and terms name from 'specialites' taxonomy. So far i'm using a filter (https://stackoverflow.com/a/59537500/19181295).
function and_extend_search( $search, &$wp_query ) {
global $wpdb;
if ( empty( $search ))
return $search;
$terms = $wp_query->query_vars[ 's' ];
$exploded = explode( ' ', $terms );
if( $exploded === FALSE || count( $exploded ) == 0 )
$exploded = array( 0 => $terms );
$search = '';
foreach( $exploded as $tag ) {
$search .= " AND (
($wpdb->posts.post_title LIKE '%$tag%')
OR EXISTS
(
SELECT
*
FROM
$wpdb->term_relationships
LEFT JOIN
$wpdb->terms
ON
$wpdb->term_relationships.term_taxonomy_id = $wpdb->terms.term_id
WHERE
$wpdb->terms.name LIKE '%$tag%'
AND
$wpdb->term_relationships.object_id = $wpdb->posts.ID
)
)";
}
return $search;
}
add_filter('posts_search', 'and_extend_search', 500, 2);
The filter is pretty good but it's searching inside all taxonomies. What i want is keeping the filter but only return results in terms associated with 'specialites' taxonomy.
Can you guys help me please ? :)
from Comment
CREATE TABLE xmo_term_relationships (
object_id bigint(20) unsigned NOT NULL DEFAULT 0,
term_taxonomy_id bigint(20) unsigned NOT NULL DEFAULT 0,
term_order int(11) NOT NULL DEFAULT 0,
PRIMARY KEY (object_id,term_taxonomy_id),
KEY term_taxonomy_id (term_taxonomy_id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci

Answer 1

If the tables are big and you want performance,
Do not use LIKE with leading wildcards
Do consider using FULLTEXT index(es).
Do install this plugin: WP Index Improvements
Get rid of the second if statement; $exploded will be as you want it anyway.
Try to avoid ORs; they do not Optimize well.
After you have done those, come back with some revised queries; I will probably have more suggestions. At that time, please provide SHOW CREATE TABLE and EXPLAIN.