新手求帮忙-SQL取数问题

假如数据量很大，下面有限列举：
F_KMBH                 F_KMJE
1001                   1000
10010010                200
10010020                200
100101000100            200
100101000200            400
2001                   2000
20010100               1000
200101000100            500
200101000200            100
200101000300            400
20010200               1000
怎么通过select取数，实现F_KMBH前8位数，如果超过8位，则前8位相同的F_KMBH求和
结果：
1001                 1000
10010010              200
10010020              200
10010100              600
2001                 2000
20010100             1000
20010200             1000