group_concat query performance


a mysql query controlling significantly slower given adding group_concat clause. currently, query looks follows:



select ... group_concat(distinct category.name) .... page where 
left outdoor join page_category page.id = page_category.page_id  
left outdoor join problem page_category.category_id = category.id
....
group page.id


as mentioned query, among others, concentration 3 tables: page, category, page_category. page compared zero churned categories. now page, page_category, problem have 9,460, 20,241 10 entries, respectively.



can anyone assistance me provoke query provoke the performance?



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