mysql update select 从查询结果中更新数据

# update select 语句(注意:必须使用inner join)
# 语法 update a inner join (select yy from b) c on a.id =c.id set a.xx = c.yy
#SELECT knowledge_id,COUNT(0) nums FROM pro_base_timu_knowledge GROUP BY knowledge_id;
UPDATE pro_base_knowledge
INNER JOIN (
SELECT
knowledge_id,
COUNT(0) nums
FROM
pro_base_timu_knowledge
GROUP BY
knowledge_id
) b ON pro_base_knowledge.id = b.knowledge_id
SET pro_base_knowledge.timu_num = b.nums