Can Anyone provide an example of RAW SQL for SELECTING posts by 2 or more tags

You seem to be catching wrong query. Dumping SQL for such URL (via posts_request filter) get me this:

SELECT SQL_CALC_FOUND_ROWS  wp_posts.* 
FROM wp_posts  
INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id) 
INNER JOIN wp_term_relationships AS tt1 ON (wp_posts.ID = tt1.object_id) 
WHERE 1=1  
AND ( wp_term_relationships.term_taxonomy_id IN (93) AND tt1.term_taxonomy_id IN (94) AND wp_posts.ID IN (
                    SELECT object_id
                    FROM wp_term_relationships
                    WHERE term_taxonomy_id IN (93,94)
                    GROUP BY object_id HAVING COUNT(object_id) = 2
                ) ) 
AND wp_posts.post_type="post" 
AND (wp_posts.post_status="publish" OR wp_posts.post_status="private") 
GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC LIMIT 0, 10

In any case see WP_Query->get_posts() method, which handles turning query variables into SQL. There is a lot of code there and a lot of it was changed in 3.1, so it’s a little hard for me to pinpoint where multiple tags are handled.

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