# 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