select * from product where vender_id = (select verder_id from product where name='Dove')
select p1.* from product p1, product p2 where p1.id = p2.id and p2.name = 'Dove'
2、根据同表字段更新
update product p1,product p2 set p1.photo_status = 2
where p1.id = p2.id and p2.photo_status is null
3、连接要有条件，否则将出现笛卡尔积
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