MySQL中DATE_FORMAT()函数的具体使用

MySQL DATE_FORMAT函数简介

要将日期值格式化为特定格式，请使用DATE_FORMAT函数。 DATE_FORMAT函数的语法如下：

DATE_FORMAT(date,format);

DATE_FORMAT()函数接受两个参数：

• date：是要格式化的有效日期值
• format：是由预定义的说明符组成的格式字符串，每个说明符前面都有一个百分比字符(%)。有关预定义说明符的列表，请参见下表。

DATE_FORMAT函数返回字符集和校对规则取决于客户端连接的设置的字符串。

下表说明了可用于构建日期格式字符串的说明符及其含义：

以下是一些常用的日期格式字符串：

MySQL DATE_FORMAT示例

我们来看看示例数据库中的orders表，其结果如下所示 -

mysql> desc orders;
+----------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra | 
+----------------+-------------+------+-----+---------+-------+
| orderNumber | int(11) | NO | PRI | NULL | |
| orderDate | date | NO | | NULL | |
| requiredDate | date | NO | | NULL | |
| shippedDate | date | YES | | NULL | |
| status | varchar(15) | NO | | NULL | |
| comments | text | YES | | NULL | |
| customerNumber | int(11) | NO | MUL | NULL | |
+----------------+-------------+------+-----+---------+-------+
7 rows in set

要选择订单的数据并格式化日期值，请使用以下语句：

SELECT
orderNumber,
DATE_FORMAT(orderdate, '%Y-%m-%d') orderDate,
DATE_FORMAT(requireddate, '%a %D %b %Y') requireddate,
DATE_FORMAT(shippedDate, '%W %D %M %Y') shippedDate
FROM
orders;

执行上面查询语句，得到以下结果 -

+-------------+------------+-------------------+------------------------------+
| orderNumber | orderDate | requireddate | shippedDate |
+-------------+------------+-------------------+------------------------------+
| 10100 | 2013-01-06 | Sun 13th Jan 2013 | Thursday 10th January 2013 |
| 10101 | 2013- 01-09 | Fri 18th Jan 2013 | Friday 11th January 2013 |
| 10102 | 2013-01-10 | Fri 18th Jan 2013 | Monday 14th January 2013 |
| 10103 | 2013- 01- 29 | Thu 7th Feb 2013 | Saturday 2nd February 2013
************* 此处省略了一大波数据 *********************************
| 10417 | 2015- 05- 13 | Tue 19th May 2015 | Tuesday 19th May 2015 |
| 10418 | 2015-05-16 | Sun 24th May 2015 | Wednesday 20th May 2015 |
| 10419 | 2015- 05- 17 | Thu 28th May 2015 | Tuesday 19th May 2015
| 10425 | 2015- 05- 31 | Sun 7th Jun 2015 | NULL |
| 10426 | 2017-07-21 | Wed 26th Jul 2017 | Sunday 23rd July 2017 |
+-------------+------------+-------------------+------------------------------+
327 rows in set

要根据格式字符串指定的不同日期格式来格式化订单日期，所需日期和每个订单的发货日期。

MySQL DATE_FORMAT与ORDER BY

请参阅以下示例：

SELECT
orderNumber,
DATE_FORMAT(shippeddate, '%W %D %M %Y') shippeddate
FROM
orders
WHERE
shippeddate IS NOT NULL
ORDER BY shippeddate;

执行上面查询语句，得到以下结果 -

+-------------+------------------------------+
| orderNumber | shippeddate |
+-------------+------------------------------+
| 10101 | Friday 11th January 2013 |
| 10156 | Friday 11th October 2013 |
| 10356 | Friday 12th December 2014 |
| 10376 | Friday 13th February 2015 |
| 10129 | Friday 14th June 2013 |
| 10279 | Friday 15th August 2014 |
| 10181 | Friday 15th November 2013 |
********* 此处省略了一大波数据 ****************
| 10348 | Wednesday 5th November 2014 |
| 10411 | Wednesday 6th May 2015 |
| 10267 | Wednesday 9th July 2014 |
| 10300 | Wednesday 9th October 2013 |
+-------------+------------------------------+
313 rows in set

在查询中，我们选择了发货日期不为NULL的所有订单，并按发货日期对订单进行排序。但是，订单未正确排序。

原因是将shippingdate用作DATE_FORMAT函数的输出的别名，它是一个字符串，ORDER BY子句根据字符串值，而不是日期值对别名进行排序。

要解决这个问题，我们必须使用不同于列名的别名; 见下列声明：

SELECT
orderNumber,
DATE_FORMAT(shippeddate, '%W %D %M %Y') 'Shipped date'
FROM
orders
WHERE
shippeddate IS NOT NULL
ORDER BY shippeddate;

执行上面查询语句，得到以下结果 -

+-------------+------------------------------+
| orderNumber | Shipped date |
+-------------+------------------------------+
| 10100 | Thursday 10th January 2013 |
| 10101 | Friday 11th January 2013 |
| 10102 | Monday 14th January 2013 |
| 10104 | Friday 1st February 2013 |
| 10103 | Saturday 2nd February 2013 |
| 10105 | Tuesday 12th February 2013 |
********* 此处省略了一大波数据 ****************
| 10413 | Saturday 9th May 2015 |
| 10415 | Tuesday 12th May 2015 |
| 10416 | Thursday 14th May 2015 |
| 10417 | Tuesday 19th May 2015 |
| 10419 | Tuesday 19th May 2015 |
| 10418 | Wednesday 20th May 2015 |
| 10426 | Sunday 23rd July 2017 |
+-------------+------------------------------+
313 rows in set

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