Mysql LEFT JOIN ON倒数第二个id

Question

我有这个问题试图总结时间：

SELECT t1.id, t1.number, t1.time - COALESCE(SUM(t2.time), 0) time FROM times t1 
LEFT JOIN times t2 ON t1.number = t2.number AND t2.id < t1.id
GROUP BY t1.id, t1.number, t1.time

输出：

id          number          time (in seconds)
--------------------------------------------
1            9              65
2            5              78
3            7              92

它工作正常，但我只需要在子句（t2.id < t1.id）中与LEFT JOIN条件的倒数第二个相加。

Answer 1

用于选择倒数第二个id

SELECT t1.id, t1.number, t1.time - COALESCE(SUM(t2.time), 0) time FROM times t1 
LEFT JOIN times t2 ON t1.number = t2.number 
AND t2.id = (select id from times order by id desc limit 1,1)
GROUP BY t1.id, t1.number, t1.time