现在有两张表:
A表:字段有,[userid int,pid int,did int,byear int,m1 int,m2 int ,m3 int,int,money decimal]
B表:字段有,[userid int ,pid int , did int , byear int ,m1 int,money decimal]
现在我要做的效果是:
  如果B表中userid,pid,did这一组合在A表中没有的,那就将此记录插入到A表中,
  如果B表中的userid,pid,did这一组合在A表中已经存在了,那就将此记录更新到A表中
请大家数据SQL语句会写的,帮忙给出这个正确的SQL语句,谢谢
我现在已经有的做法是:
这是更新语句,可以得到正确结果:
update a set m1=b.m1,money=b.money from  b where b.userid=a.userid and b.pid=a.pid and b.did=a.did and b.byear=a.byear

这是插入语句,但无法得到想要的结果:
insert into a (userid,pid,did,byear,m1,money) select b.userid,b.pid,b.did,b.byear,b.m1,b.money from b
  where not exists (select b1.userid,b1.pid,b1.did,b1.byear,b1.m1,b1.money from b as b1 ,a as a1
                     where b1.userid=a1.userid and b1.pid=a1.pid and b1.did=a1.did)