Q&A for speakers of other languages learning English
with tag_combinations as ( select pt.postid, string_agg(t.tagname, ', ') within group (order by t.tagname) as tag_combination from posttags pt join tags t on pt.tagid = t.id group by pt.postid ), tag_combination_count as ( select tag_combination, count(postid) as post_count from tag_combinations group by tag_combination ) select top 1 tag_combination, post_count from tag_combination_count order by post_count desc;