Question

我正在为一个客户端开发一个小项目，数据库中的数据让我有点麻烦。我正在从数据库中填写付费分期付款的搜索表单。我可以把数据弄好，它的日期字段让我烦恼。

每个分期的日期，月份和年份都有单独的字段。有没有办法可以在合并的字段中使用CONCAT或DATE或甚至使用CAST来搜索数据。

我试过以下

SELECT DATE_FORMAT( CONCAT( received_date, received_month, received_year ) ,  '%d/%m/%Y' ) FROM policy_installments

和

SELECT DATE_FORMAT(STR_TO_DATE(CONCAT('pit.received_date', '-', 'pit.received_month','-', 'pit.received_year'), '%d-%m-%Y') AS mydate, '%d-%m-%Y') AS modate FROM policy_installments pit ORDER BY mydate

和

SELECT * FROM policy_installments WHERE CONCAT(CAST(received_date AS CHAR),"-",CAST(received_month AS CHAR),"-",CAST(received_year AS CHAR)) >= '1-1-2014' AND CONCAT(CAST(received_date AS CHAR),"-",CAST(received_month AS CHAR),"-",CAST(received_year AS CHAR)) <= '31-3-2014'

当我使用以下内容时，我会得到一些意想不到的数据：

SELECT CONCAT_WS( received_date,  "-", received_month,  "-", received_year ) FROM policy_installments

RESULT

2d313130312d3132303039
2d3237313032372d323732303039 etc etc

3个字段中的每一个都是INT(11)类型。

然而，这些都没有给我正确的数据。有没有办法我可以转换所有3个字段并使用日期传递到查询，以使我能够正确地获取正确的数据？

非常感谢任何帮助！

Answer 1

要将连接字符串转换为日期，字符串的格式应与您用于转换的格式相同。

对于dd/mm/yyyy格式的日期字符串，应使用%d/%m%Y格式转换为sql日期。

示例：

SELECT STR_TO_DATE( 
         CONCAT( received_date, '/', received_month, '/', received_year ),
         '%d/%m/%Y' 
       ) as rcvd_date
FROM policy_installments

要与其他日期进行比较，您可以使用BETWEEN子句。

示例：

SELECT * FROM policy_installments 
WHERE 
    STR_TO_DATE( 
      CONCAT( received_date, '-', received_month, '-', received_year ),
      '%d-%m-%Y' 
    ) BETWEEN STR_TO_DATE( '1-1-2014', '%d-%m-%Y' ) 
          AND STR_TO_DATE( '31-3-2014', '%d-%m-%Y' )

请参阅：
MySQL: STR_TO_DATE(str,format)：将字符串转换为日期

Answer 2

通常，您希望避免在列上执行该功能。而是在文字上执行该功能，以便您可以利用列上的索引：

SELECT *
FROM policy_installments 
WHERE received_year = YEAR('2014-03-31')
  AND received_month = MONTH('2014-03-31')
  AND received_date = DAY('2014-03-31')

在received_year，received_month和received_date上添加多列索引，你会做得很好。

显然，此方法仅适用于=比较。对于<=，它变得有点复杂：

SELECT *
FROM policy_installments 
WHERE 
  received_year < YEAR('2014-03-31')
UNION 
SELECT *
FROM policy_installments 
WHERE 
  received_year = YEAR('2014-03-31')
  AND received_month < MONTH('2014-03-31')
UNION 
SELECT *
FROM policy_installments 
WHERE 
  received_year = YEAR('2014-03-31')
  AND received_month = MONTH('2014-03-31')
  AND received_date <= DAY('2014-03-31')

但是这个较长的查询仍然可以使用索引。

为简化起见，请考虑创建一个实际的日期列，并使用适当的值更新它。

Mysql - Concat多个INT字段一起构成DATE字段

2 个答案: