如何使用Min()函数?

比如有如下数据:
ItemID ToolModule PmType SetDate T TFlag
201100201014 DWPRS07@AllModule W_P 2011-11-28 7 AY
201100201015 DWPRS07@AllModule W_P 2011-12-5 7 AY
201100201016 DWPRS07@AllModule W_P 2011-12-12 7 AY
201100201017 DWPRS07@AllModule W_P 2011-12-19 7 AY
201100201018 DWPRS07@AllModule W_P 2011-12-26 7 AY
201200201001 DWPRS07@AllModule M_P 2012-1-2 7 AY
201100212001 DWPRS07@AllModule M_P 2011-8-29 30 AY
201100212002 DWPRS07@AllModule M_P 2011-9-28 30 AY
201100212003 DWPRS07@AllModule Q_P 2011-10-28 30 AY
201100212004 DWPRS07@AllModule Q_P 2011-11-27 30 AY

通过 搜索语句搜索到:
ItemID ToolModule PmType SetDate T TFlag
201100201014 DWPRS07@AllModule W_P 2011-11-28 7 AY
201200201001 DWPRS07@AllModule M_P 2012-1-2 7 AY
201100212003 DWPRS07@AllModule Q_P 2011-10-28 30 AY

如何写这个语句呢...
(PmType为不同的，SetDate取 最小日期的数据，)

SQL code

select * from tb a where not exists(select 1 from tb where PmType=a.PmType and SetDate<a.SetDate)

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