求一条SQl语句????????
A B C
a001 2006-1-1
a001 10 2006-2-1
a001 30 2006-3-1
a001 20 2006-4-1
b001 2005-1-1
b001 30 2006-2-1
b001 25.5 2006-3-1
c001 2007-3-1
c001 30 2006-5-1
c001 15 2007-2-1
c001 50 2007-1-1
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结果:
A B C
a001 20 2006-4-1
b001 25.5 2006-3-1
c001 15 2007-2-1
取出C列中时间最大的并且B 不为空的记录(不能有A重复的记录)