将mysql列解释为日期间隔单位?

wztqucjr  于 2021-07-24  发布在  Java
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在mysql中使用date和time函数时,比如date\u add,是否可以将间隔单位存储在列中并在查询中使用?
例如,考虑下表:

+---------------------------+---------------------------------------------------+------+-----+---------+----------------+
| Field                     | Type                                              | Null | Key | Default | Extra          |
+---------------------------+---------------------------------------------------+------+-----+---------+----------------+
| snapshotSchedule_entry_id | int(10) unsigned                                  | NO   | PRI | NULL    | auto_increment |
| snapshotSchedule_id       | int(10) unsigned                                  | NO   | PRI | NULL    |                |
| everyFrequency            | smallint(5) unsigned                              | NO   |     | NULL    |                |
| everyInterval             | enum('minute','hour','day','week','month','year') | NO   |     | NULL    |                |
| afterFrequency            | smallint(5) unsigned                              | NO   |     | NULL    |                |
| afterInterval             | enum('minute','hour','day','week','month','year') | NO   |     | NULL    |                |
+---------------------------+---------------------------------------------------+------+-----+---------+----------------+

以下查询工作正常,因为它只处理区间表达式:

select * from snapshotSchedule_entry order by date_add(now(), interval everyFrequency month);

当我想处理间隔单位(例如月、年等)时,它不会解释它。
mysql>select*from snapshotschedule\u entry order by date\u add(now(),interval 1 everyinterval);错误1064(42000):您的sql语法有错误;在第1行的“everyinterval”附近,检查与mysql服务器版本相对应的手册,以获得正确的语法
我对这种行为并不感到惊讶,我只是好奇这是否可行。在代码中这样做并不是世界末日,但我想知道这是否可能。

g6ll5ycj

g6ll5ycj1#

mysql对于区间表达式没有那么灵活。你需要一个大的 case 具有硬编码值的表达式:

order by case everyInterval
    when  'minute' then now() + inteval everyFrequency minute
    when  'hour'   then now() + inteval everyFrequency hour
    when  'day'    then now() + inteval everyFrequency day
    when  'week'   then now() + inteval everyFrequency week
    when  'month'  then now() + inteval everyFrequency month
    when  'year'   then now() + inteval everyFrequency year
end

一个更简单的替代方法是重新设计模式,以固定频率(比如秒和月)存储间隔。你可以这样做:

order by now() 
    + interval everyFrequencySecond second
    + interval everyFrequencyMonth  month

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