该条语句运行好久，什么有关问题，该怎么优化

该条语句运行好久，什么问题，该如何优化
update user_score set score=(score+5)
where acc_nbr in (select calling_nbr from tb_up50_call where calling_nbr!=called_nbr
 group by calling_nbr);

是score=(score+5)计算，和acc_nbr in还有group by 的问题么？
谢谢解答！

[解决办法]
update user_score ,(select calling_nbr from tb_up50_call where calling_nbr!=called_nbr) b
set score=(score+5)
where acc_nbr=calling_nbr
[解决办法]
--如果索引都加了，用exists效率应该会高些
update user_score set score=(score+5)
where acc_nbr exists (select calling_nbr from tb_up50_call where calling_nbr!=called_nbr
 group by calling_nbr);