Build A Custom SQL Query for WordPress Search

A possible solution is to use the pre_get_posts action:

add_action('pre_get_posts', 'custom_search_query');

function custom_search_query($query) {

  // run only if is a search query and if the search string is not empty
  if($query->is_search() && $query->is_main_query() && get_query_var('s', false)) {

    // here you can use your custom query having 'get_query_var('s', false)' as $Search string
    //"SELECT SQL_CALC_FOUND_ROWS *..........
    
    // just modify your query to return only the IDS of the posts found and put them in an array $ids
    $ids=[1,2,3,4]; // example of IDS found by your custom query
    
    // unset the query_var otherwise the custom SQL will not work
    unset( $query->query_vars['s'] );

    // set the IDS as 'post__in' in the $query
    $query->set( 'post__in', $ids );
  }
}

Having removed the $query->query_vars['s'] the only missing thing will be the searched string in the template file ‘search.php’ where, normally, there will be something like: ( from twentytwentyone theme)

<h1 class="page-title">
<?php
printf(
    /* translators: %s: Search term. */
    esc_html__( 'Results for "%s"', 'twentytwentyone' ),
    '<span class="page-description search-term">' . esc_html( get_search_query() ) . '</span>'
    );
?>
</h1>

So get_search_query() will print an empty string instead of the searched string, just replace the get_search_query() function with $_GET['s']

Related Posts: