在计算日期时如何使用 ORDER BY 子句？

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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