如果我们在计算日期时使用 ORDER BY 子句,查找记录会更方便。为了理解它,我们从表“Collegedetail”中获取数据,如下 -
mysql> Select * from Collegedetail; +------+---------+------------+ | ID | Country | Estb | +------+---------+------------+ | 111 | INDIA | 2010-05-01 | | 130 | INDIA | 1995-10-25 | | 139 | USA | 1994-09-25 | | 1539 | UK | 2001-07-23 | | 1545 | Russia | 2010-07-30 | +------+---------+------------+ 5 rows in set (0.00 sec)
现在,假设我们想计算一所大学的历史年数,那么可以按如下方式完成 -
mysql> Select ID, estb, CURDATE(),((YEAR(CURDATE())-YEAR(estb))-(RIGHT(CURDATE(),5)<RIGHT(estb,5))) AS 'YEARS_OLD' from collegedetail; +------+------------+------------+-----------+ | ID | estb | CURDATE() | YEARS_OLD | +------+------------+------------+-----------+ | 111 | 2010-05-01 | 2017-11-30 | 7 | | 130 | 1995-10-25 | 2017-11-30 | 22 | | 139 | 1994-09-25 | 2017-11-30 | 23 | | 1539 | 2001-07-23 | 2017-11-30 | 16 | | 1545 | 2010-07-30 | 2017-11-30 | 7 | +------+------------+------------+-----------+ 5 rows in set (0.00 sec)
如果我们在计算大学成立年数时使用如下 ORDER BY 子句,我们的搜索会更方便 -
mysql> Select ID, estb, CURDATE(),((YEAR(CURDATE())-YEAR(estb))-(RIGHT(CURDATE(),5)<RIGHT(estb,5))) AS 'YEARS_OLD' from collegedetail ORDER BY YEARS_OLD; +------+------------+------------+-----------+ | ID | estb | CURDATE() | YEARS_OLD | +------+------------+------------+-----------+ | 111 | 2010-05-01 | 2017-11-30 | 7 | | 1545 | 2010-07-30 | 2017-11-30 | 7 | | 1539 | 2001-07-23 | 2017-11-30 | 16 | | 130 | 1995-10-25 | 2017-11-30 | 22 | | 139 | 1994-09-25 | 2017-11-30 | 23 | +------+------------+------------+-----------+ 5 rows in set (0.01 sec)
上面的结果集显示,我们可以通过使用带有“YEARS_OLD”的 ORER BY 子句非常轻松地搜索最古老的大学。我们还可以将 DESC 关键字与 ORDER BY 子句一起使用,该子句返回顶行中最古老的大学,如下所示 -
mysql> Select ID, estb, CURDATE(),((YEAR(CURDATE())-YEAR(estb))-(RIGHT(CURDATE(),5)<RIGHT(estb,5))) AS 'YEARS_OLD' from collegedetail ORDER BY YEARS_O LD DESC; +------+------------+------------+-----------+ | ID | estb | CURDATE() | YEARS_OLD | +------+------------+------------+-----------+ | 139 | 1994-09-25 | 2017-11-30 | 23 | | 130 | 1995-10-25 | 2017-11-30 | 22 | | 1539 | 2001-07-23 | 2017-11-30 | 16 | | 111 | 2010-05-01 | 2017-11-30 | 7 | | 1545 | 2010-07-30 | 2017-11-30 | 7 | +------+------------+------------+-----------+ 5 rows in set (0.00 sec)
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