极客教程MySQL 如何在计算日期时使用ORDER BY子句？
如果我们在计算日期时使用ORDER BY子句，那么查找记录将更加方便。 为了理解此点，我们从表“Collegedetail”中获取以下数据-
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，假设我们想要计算一个学院有多少年历史，那么可以按以下方式完成-
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)
如果我们在计算一个学院有多少年历史时使用ORDER BY子句，那么我们的搜索会更加方便，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_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)
以上结果集显示我们可以通过使用’YEARS_OLD’与ORER BY子句来轻松搜索最古老的学院。 我们还可以使用ORDER BY子句的DESC关键字，返回最古老的学院，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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