Tạo thêm một cột trong table post và tìm kiếm nội dung của chúng (ok) có một cách khác dùng js :(

C:\xampp\htdocs\wordpress4\wp-content\themes\twentytwentyone-child\functions.php

<?php
// Add the custom columns to the post post type:
add_filter('manage_post_posts_columns', 'set_custom_edit_post_columns');
function set_custom_edit_post_columns($columns) {
  $columns['publisher']   = __('Publisher', 'your_text_domain');
  return $columns;
}
// Add the data to the custom columns for the post post type:
add_action('manage_post_posts_custom_column', 'custom_post_column', 10, 2);
function custom_post_column($column, $post_id) {
  switch ($column) {
  case 'publisher':
    echo get_post_meta($post_id, 'publisher', true);
    break;
  }
}
//Register Meta box
add_action( 'add_meta_boxes', function() {
    add_meta_box( 'wpdocs-id', 'Social link', 'wpdocs_field_cb', 'post', 'side' );
} );
//Meta callback function
function wpdocs_field_cb( $post ) {
  $wpdocs_meta_val = get_post_meta( $post->ID, 'publisher', true );
  ?>
    <input type="text" name="publisher" value="<?php echo esc_attr( $wpdocs_meta_val ) ?>">
  <?php
}
//save meta value with save post hook
add_action( 'save_post', function( $post_id ) {
  if ( isset( $_POST['publisher'] ) ) {
    update_post_meta( $post_id, 'publisher', $_POST['publisher'] );
  }
} );
if (!class_exists('parse_search_custom') && is_admin()) {
  global $test;
  class parse_search_custom {
    function parse_search($s) {
      $q      = array();
      $newout = str_replace(array(' ', '　'), ' ', urldecode($s));
      $q['s'] = $newout;
      global $wpdb;
      $search = '';
      // Added slashes screw with quote grouping when done early, so done later.
      $q['s'] = stripslashes($q['s']);
      if (empty($_GET['s']) && is_main_query()) {
        $q['s'] = urldecode($q['s']);
      }
      // There are no line breaks in <input /> fields.
      $q['s']                  = str_replace(array("\r", "\n"), '', $q['s']);
      $q['search_terms_count'] = 1;
      if (!empty($q['sentence'])) {
        $q['search_terms'] = array($q['s']);
      } else {
        if (preg_match_all('/".*?("|$)|((?<=[\t ",+])|^)[^\t ",+]+/', $q['s'], $matches)) {
          $q['search_terms_count'] = count($matches[0]);
          $q['search_terms']       = $this->parse_search_terms($matches[0]);
          // If the search string has only short terms or stopwords, or is 10+ terms long, match it as sentence.
          if (empty($q['search_terms']) || count($q['search_terms']) > 9) {
            $q['search_terms'] = array($q['s']);
          }
        } else {
          $q['search_terms'] = array($q['s']);
        }
      }
      $n                         = !empty($q['exact']) ? '' : '%';
      $searchand                 = '';
      $q['search_orderby_title'] = array();
      /**
       * Filters the prefix that indicates that a search term should be excluded from results.
       *
       * @since 4.7.0
       *
       * @param string $exclusion_prefix The prefix. Default '-'. Returning
       *                                 an empty value disables exclusions.
       */
      $exclusion_prefix = apply_filters('wp_query_search_exclusion_prefix', '-');
      foreach ($q['search_terms'] as $term) {
        // If there is an $exclusion_prefix, terms prefixed with it should be excluded.
        $exclude = $exclusion_prefix && (substr($term, 0, 1) === $exclusion_prefix);
        if ($exclude) {
          $like_op  = 'NOT LIKE';
          $andor_op = 'AND';
          $term     = substr($term, 1);
        } else {
          $like_op  = 'LIKE';
          $andor_op = 'OR';
        }
        if ($n && !$exclude) {
          $like                        = '%' . $wpdb->esc_like($term) . '%';
          $q['search_orderby_title'][] = $wpdb->prepare("{$wpdb->postmeta}.meta_value LIKE %s", $like);
        }
        $like = $n . $wpdb->esc_like($term) . $n;
        $search .= $wpdb->prepare("{$searchand}((({$wpdb->postmeta}.meta_value $like_op %s) OR ({$wpdb->posts}.post_title $like_op %s)) AND {$wpdb->posts}.post_status = 'publish' )", $like, $like);
        $searchand = ' OR ';
      }
      return $search;
    }
    function parse_search_terms($terms) {
      $strtolower = function_exists('mb_strtolower') ? 'mb_strtolower' : 'strtolower';
      $checked    = array();
      $stopwords  = $this->get_search_stopwords();
      foreach ($terms as $term) {
        // Keep before/after spaces when term is for exact match.
        if (preg_match('/^".+"$/', $term)) {
          $term = trim($term, "\"'");
        } else {
          $term = trim($term, "\"' ");
        }
        // Avoid single A-Z and single dashes.
        if (!$term || (1 === strlen($term) && preg_match('/^[a-z\-]$/i', $term))) {
          continue;
        }
        if (in_array(call_user_func($strtolower, $term), $stopwords, true)) {
          continue;
        }
        $checked[] = $term;
      }
      return $checked;
    }
    function get_search_stopwords() {
      /*
       * translators: This is a comma-separated list of very common words that should be excluded from a search,
       * like a, an, and the. These are usually called "stopwords". You should not simply translate these individual
       * words into your language. Instead, look for and provide commonly accepted stopwords in your language.
       */
      $words = explode(
        ',', _x('about,an,are,as,at,be,by,com,for,from,how,in,is,it,of,on,or,that,the,this,to,was,what,when,where,who,will,with,www', 'Comma-separated list of search stopwords in your language')
      );
      $stopwords = array();
      foreach ($words as $word) {
        $word = trim($word, "\r\n\t ");
        if ($word) {
          $stopwords[] = $word;
        }
      }
      /**
       * Filters stopwords used when parsing search terms.
       *
       * @since 3.7.0
       *
       * @param string[] $stopwords Array of stopwords.
       */
      $stopwords = apply_filters('wp_search_stopwords_ct', $stopwords);
      return $stopwords;
    }
  }
  $test = new parse_search_custom();
}
function custom_posts_join($join){
  global $wpdb;
  if(is_admin()) {
    $join = " LEFT JOIN {$wpdb->postmeta} ON {$wpdb->posts}.ID = {$wpdb->postmeta}.post_id ";
  }
  return $join;
}
add_filter( 'posts_join' , 'custom_posts_join');
add_filter( 'posts_where' , 'posts_where',10,2 );
function posts_where( $where, $query ) {
  global $wpdb, $test;
  if($query->is_admin && $query->is_search) {
    $string = $query->query_vars['s'];
    $tests = $test->parse_search($string);
    $where = " AND $tests ";
  }
  return $where;
}
add_filter('posts_groupby', 'my_posts_groupby');
function my_posts_groupby($groupby) {
  global $wpdb;
  $groupby = " {$wpdb->posts}.ID ";
  return $groupby;
}
?>

Có cách dùng tablesorter qúa tuyệt vời hơn đã có bài viết tôi viết về nó

https://mottie.github.io/tablesorter/docs/#Demo