INSERT INTO T VALUES('2004-1-29','PLM248');
INSERT INTO T VALUES('2004-12-12','PLNER3');
INSERT INTO T VALUES('2004-11-11','PLM248');
INSERT INTO T VALUES('2004-11-21','PLM248');
SELECT * FROM T;
SELECT MAX(日期)AS 日期,任务单 FROM T AS T2 GROUP BY 任务单
UNION
SELECT MIN(日期)AS 日期,任务单 FROM T AS T1 GROUP BY 任务单
INSERT INTO T VALUES(2004-1-29,'PLM248');
INSERT INTO T VALUES(2004-12-12,'PLNER3');
INSERT INTO T VALUES(2004-11-11,'PLM248');
INSERT INTO T VALUES(2004-11-21,'PLM248');
SELECT * FROM T;
SELECT MAX(日期)AS 日期,任务单 FROM T AS T2 GROUP BY 任务单
UNION
SELECT MIN(日期)AS 日期,任务单 FROM T AS T1 GROUP BY 任务单
保留最大日期的:
select * from 表 as a where not exists (select * from 表 where 任务单=a.任务单 and 日期>a.日期)
保留最小日期的:
select * from 表 as a where not exists (select * from 表 where 任务单=a.任务单 and 日期<a.日期)