varchar日期时间比较问题

Question

I have a legacy table which has a varchar column represent date, format is MM/DD/YYYY (eg 01/08/2015). It is not convenient to perform data range selection since it is a varchar (when I use < or > kinds comparison, it goes to varchar/string comparison, which have different results from date comparision).

For example, I want to select only rows which dates are between 01/08/2015 and 01/10/2015. Any smart solution is appreciated, and I cannot change the data type of varchar to date in my existing table.

I am using MySQL Workbench/MySQL.

Answer 1

Varchar dates are evil and they are not real date, the best solution is to use mysql's native date data types.

Since you can't change the datatype you may use str_to_date() function and here how it works

mysql> select str_to_date('01/08/2015','%d/%m/%Y') as d ;
+------------+
| d          |
+------------+
| 2015-08-01 |
+------------+

So the query for select would be

select * from table_name
where
str_to_date(date_column,'%d/%m/%Y')
between
str_to_date('01/08/2015','%d/%m/%Y')
and
str_to_date('01/10/2015','%d/%m/%Y')

Answer 2

您可以使用STR_TO_DATE将日期转换为字符串：

STR_TO_DATE(yourdatefield, '%m/%d/%Y')

Answer 3

SELECT STR_TO_DATE(got_fired_at, '%m/%d/%Y') BETWEEN ? AND ? FROM firings;

（字段/表名保证随机选择）

Answer 4

There are many answers which addresses many different way of converting the string to date.

You may choose whichever is perfect for your need

SELECT * FROM `your_table` WHERE DATE_FORMAT(my_column_with_the_string_date, "%Y-%m-%d") <= '2011-09-30'

DATE_FORMAT can be used to convert your date string to any format: I will use the NOW() function instead of string to list different formats that are supported

DATE_FORMAT(NOW(),'%b %d %Y %h:%i %p')
DATE_FORMAT(NOW(),'%m-%d-%Y')
DATE_FORMAT(NOW(),'%d %b %y')
DATE_FORMAT(NOW(),'%d %b %Y %T:%f')

The output of the above is:

Nov 04 2014 11:45 PM
11-04-2014
04 Nov 14
04 Nov 2014 11:45:34:243

You can modify your query accordingly

Answer 5

使用MySQL的STR_TO_DATE函数将日期字符串解析为日期对象，然后进行比较。