declare @t table 
(日期 varchar(10),站点 varchar(4),最高 varchar(4),最低 varchar(4))
insert into @t
select '20000101','长沙','0001','-003' union all
select '20000102','长沙','0121','0080' union all
select '20000103','长沙','0131','0050' union all
select '20000104','长沙','0351','0230' union all
select '20000101','湘潭','0021','0010' union all
select '20000102','湘潭','0231','0002' union all
select '20000103','湘潭','0121','0008' union all
select '20000101','株洲','0021','001' union all
select '20000102','株洲','0231','002' union all
select '20000103','株洲','0121','003'

select a.站点,
a.c1 as 'max(最高)',
(select max(日期) from @t where 最高=c1 and 站点=a.站点) as 'max(最高)出现时间',
a.c2 as 'min(最高)',
(select max(日期) from @t where 最高=c2 and 站点=a.站点) as 'min(最高)出现时间',
a.c3 as 'max(最低)',
(select max(日期) from @t where 最低=c3 and 站点=a.站点) as 'max(最低)出现时间',
a.c4 as 'min(最低)',
(select max(日期) from @t where 最低=c4 and 站点=a.站点) as 'min(最低)出现时间'
from 
(
    select 站点,
    max(最高) as c1,min(最高) as c2,max(最低) as c3,min(最低) as c4
    from @t t group by 站点
) a

--我帮你改了列名和顺序，你把表名和你的对应了即可
/*
站点   max(最高) max(最高)出现时间 min(最高) min(最高)出现时间 max(最低) max(最低)出现时间 min(最低) min(最低)出现时间
---- ------- ----------- ------- ----------- ------- ----------- ------- -----------
长沙   0351    20000104    0001    20000101    0230    20000104    -003    20000101
湘潭   0231    20000102    0021    20000101    0010    20000101    0002    20000102
株洲   0231    20000102    0021    20000101    003     20000103    001     20000101
*/