根据主键,把一个表的字段赋值到另一张表
需求:根据userId 把user表的 username 和phone字段填充到score表中
update score,user set score.username = user.username , score.phone = user.phone where score.userId = user.userId
或者
update score join user on score.userId=user.userId set score.username = user.username , score.phone = user.phone