老问题，关于消除重复记录的问题
field1|field2|field3
客户1 |07-01-12 |事项1
客户1 |07-01-13 |事项2
客户2 |07-01-15 |事项3
客户4 |07-01-16 |事项4
要求只查出：
客户1 |07-01-13 |事项2
客户2 |07-01-15 |事项3
客户4 |07-01-16 |事项4
两条记录，就是只取日期最新的记录，该如何？
[解决办法]
select * from tablename a
where not exists (select 1 from tablename where field1 = a.field1 and field2 > a.field2)
[解决办法]
select * from tbName as A
where not exists(select 1 from tbName where field1=A.field1 and field2> A.field1)
