对一字段进行分组，且时间最大。sql如何写？没分了

对一字段进行分组，且时间最大。sql怎么写？没分了。
测试SQL

SQL code

CREATE TABLE test.dbo.ST_WAS_R (    ID varchar(50) NOT NULL,    STCD char(8) NOT NULL,    TM datetime NOT NULL,    UPZ numeric(7,3) NOT NULL,    DWZ numeric(7,3) NOT NULL,    TGTQ numeric(9,3) NOT NULL,    SWCHRCD char(1),    SUPWPTN char(1),    SDWWPTN char(1),    MSQMT char(1),    PRIMARY KEY (ID))GOINSERT INTO test.dbo.ST_WAS_R(ID, STCD, TM, UPZ, DWZ, TGTQ, SWCHRCD, SUPWPTN, SDWWPTN, MSQMT) VALUES ('1', 'TST00001', '2012-07-17 11:00:00.0', 2.000, 1.000, 1.000, null, null, null, null)GOINSERT INTO test.dbo.ST_WAS_R(ID, STCD, TM, UPZ, DWZ, TGTQ, SWCHRCD, SUPWPTN, SDWWPTN, MSQMT) VALUES ('2', 'TST00002', '2012-07-17 00:00:00.0', 1.000, 1.000, 1.000, null, null, null, null)GOINSERT INTO test.dbo.ST_WAS_R(ID, STCD, TM, UPZ, DWZ, TGTQ, SWCHRCD, SUPWPTN, SDWWPTN, MSQMT) VALUES ('3', 'TST00001', '2012-07-17 00:00:00.0', 1.000, 1.000, 1.000, null, null, null, null)GOINSERT INTO test.dbo.ST_WAS_R(ID, STCD, TM, UPZ, DWZ, TGTQ, SWCHRCD, SUPWPTN, SDWWPTN, MSQMT) VALUES ('4', 'TST00003', '2012-07-18 00:00:00.0', 2.000, 2.000, 2.000, null, null, null, null)GOINSERT INTO test.dbo.ST_WAS_R(ID, STCD, TM, UPZ, DWZ, TGTQ, SWCHRCD, SUPWPTN, SDWWPTN, MSQMT) VALUES ('5', 'TST00004', '2012-07-15 00:00:00.0', 3.000, 3.000, 3.000, null, null, null, null)GO

SQL code

select a.stcd,tm,upzfrom ST_WAS_R a, (select stcd,max(tm) mtm from ST_WAS_R group by stcd )b  where a.stcd=b.STCD and a.tm=b.mtm
[解决办法]
SQL code
select a.stcd,tm,upzfrom ST_WAS_R a,(select stcd,max(tm) mtmfrom ST_WAS_Rgroup by stcd)b  where a.stcd=b.STCD and a.tm=b.mtm