如何将字符转义为sql查询db

Can you help me with proper syntax of this piece of code? I want use a table prefix variable {$wpdb->prefix}, but I don't know how to proper escape double quotes.

 $the_query = 
                                  "
                                     SELECT 
                                        {$wpdb->prefix}frm_items.id AS store_id,
                                        MAX(IF({$wpdb->prefix}frm_item_metas.field_id = 224, {$wpdb->prefix}frm_item_metas.meta_value,\"\"))  prvni,
                                        MAX(IF({$wpdb->prefix}frm_item_metas.field_id = 225, {$wpdb->prefix}frm_item_metas.meta_value,\"\"))  druhy,
                                        MAX(IF({$wpdb->prefix}frm_item_metas.field_id = 226, {$wpdb->prefix}frm_item_metas.meta_value,\"\"))  treti,

                                      FROM 
                                        {$wpdb->prefix}frm_items,
                                        {$wpdb->prefix}frm_item_metas
                                      WHERE
                                          {$wpdb->prefix}frm_items.id = {$wpdb->prefix}frm_item_metas.item_id
                                       AND
                                        {$wpdb->prefix}frm_item_metas.field_id
                                        IN

                                        ( 224,225,226 )

                                      GROUP BY
                                        {$wpdb->prefix}frm_items.id

                                      ORDER BY

                                        {$wpdb->prefix}frm_item_metas.field_id = 224 DESC,
                                        {$wpdb->prefix}frm_item_metas.field_id = 225 DESC,          
                                        {$wpdb->prefix}frm_item_metas.field_id = 226 DESC



                                   "

      ;

Mayby you should try this:

        $table_name = $wpdb->prefix . 'frm_items';
        $query = "SELECT $table_name.id AS store_id.... "

Like this?

$theQuery = "SELECT ".$wpdb->prefix."frm_items.id AS store_id, 

MAX(IF(".$wpdb->prefix."frm_item_metas.field_id = 224, ".$wpdb->prefix."frm_item_metas.meta_value,\"\"))  prvni,
MAX(IF(".$wpdb->prefix."frm_item_metas.field_id = 225, ".$wpdb->prefix."frm_item_metas.meta_value,\"\"))  druhy,
MAX(IF(".$wpdb->prefix."frm_item_metas.field_id = 226, ".$wpdb->prefix."frm_item_metas.meta_value,\"\"))  treti,

FROM 
    ".$wpdb->prefix."frm_items,
    ".$wpdb->prefix."frm_item_metas
WHERE
    ".$wpdb->prefix."frm_items.id = ".$wpdb->prefix."frm_item_metas.item_id
AND
     ".$wpdb->prefix."frm_item_metas.field_id
IN
     ( 224,225,226 )

GROUP BY
     ".$wpdb->prefix."frm_items.id

ORDER BY

       ".$wpdb->prefix."frm_item_metas.field_id = 224 DESC,
       ".$wpdb->prefix."frm_item_metas.field_id = 225 DESC,          
       ".$wpdb->prefix."frm_item_metas.field_id = 226 DESC;