title: And condition on multi-valued attribute filter value
body: <p>Here is the structure of my database with products and categories</p>
  
  <p>-- Product Table</p>
  
  <pre><code>CREATE TABLE `product_table` (
  `product_id` int(11) NOT NULL,
  `product_title` text,
  `product_description` text
  );
  </code></pre>
  
  <p>-- Product2Category Table</p>
  
  <pre><code>CREATE TABLE `product2category_table` (
  `product_id` int(11) NOT NULL,
  `category_id` int(11) NOT NULL
  );
  </code></pre>
  
  <p>I am creating the multi-valued attribute on category</p>
  
  <pre><code>sql_attr_multi = uint prod_cat from query; \
  select p.product_id, c.category_id from product as p, product2category as c
              where c.product_id = p.product_id;
  </code></pre>
  
  <p>The relation between product and categories is many to many. As an example a product called lenovo can belong to categories:</p>
  
  <pre><code>category_id category_title
      12           sturdy
      20           laptop
  </code></pre>
  
  <p>Question: How should I query using php-sphinx api, find all the products with electronics in their description belonging to both the categories ids 12 and 20. Normally $cl->setfilter('prod_cat',array(12,20) will return even the products belonging to either of the categories. I know if I group concatenate all the categories for a product and do the full text search, it is quite simple. But is there a way to handle with the MVA feature.</p>