【问题】
I have a table structured like this

index   date time status
1 2015-01-01 13:00:00 start
2 2015-01-01 13:10:00 continue
3 2015-01-01 13:20:00 continue
4 2015-01-01 13:30:00 end
5 2015-01-01 13:30:00 ready
6 2015-01-01 13:40:00 start
7 2015-01-01 13:50:00 continue
8 2015-01-01 15:00:00 end`

and what I would like to do is count the time between start and end (ie. index 1-4 is 30min, 6-8 is 20min), but taking into account only the first start and first end, so that the query doesn’t choose the time difference of index 1-8. Which query is used to calculate time difference between two statues (start-end) and show the result for multiple instances of start-end without them getting batched into one event?

正确答案：

SELECT x.*

 , TIMEDIFF(MIN(y.dt),x.dt)diff

 FROM my_table x

 JOIN my_table y

 ON y.dt >= x.dt

WHERE x.status = 'start'

 AND y.status = 'end'

GROUP

 BY x.id;

【回答】

SQL 做这种有序的运算很麻烦，所以可以选用集算器来实现，代码简单易懂：

集算器提供 JDBC 接口，可以像数据库一样嵌入到应用程序中，用起来很简单，可参考Java 如何调用 SPL 脚本。