php mysql query with GROUP_CONCAT & if statement

i write a sql query in php

SELECT wp_news_contents.*,(SELECT GROUP_CONCAT('wp_news_tags.tag_id=',tag_id SEPARATOR ' || ') FROM wp_news_tags WHERE content_id= 1)AS sumset FROM wp_news_contents,wp_news_tags WHERE wp_news_contents.id = wp_news_tags.content_id AND wp_news_tags.content_id != '1' GROUP BY wp_news_contents.id ORDER BY (SUM(IF(sumset ,1,0))) DESC LIMIT 0,5

sumset is true : wp_news_tags.tag_id=777 || wp_news_tags.tag_id=529

but "if statement" not working.what is wrong & how to solve it