php - Mysql GROUP_CONCAT is extremely slow -


i have table in database 450.000 rows.

why query extremely slow? can fix it?

select `art_article_nr`, `name`, `sup_brand`, `path`, `cross_type_no`, group_concat(`categ` order `str_level` asc separator '>>') categ2 tof_articles2 limit 9

looks doing full table scan, add index if not done yet

alter table tof_articles2 add index str_leve_idx(str_leve)


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