经过explain排查，一段很长的sql中的瓶颈sql为：

SELECT scf.specode, scf.new_num AS ending_num, scf.new_price AS endingPrice, scf.new_fee AS endingFee
        FROM (
                SELECT scf.specode, scf.new_num, scf.new_price, scf.new_fee
                FROM sku_cost_flow scf
                WHERE scf.specode IN (
                             ......
                        )
                        AND scf.time <= UNIX_TIMESTAMP('2023-06-30 23:59:59')
                ORDER BY time DESC, id DESC
                LIMIT 100000000
        ) scf
        GROUP BY scf.specode

这里子查询 limit 10000000 实在是太大了，也不知道之前的是怎么写的，主要还是查出每个specode对应的最近时间的一些数据，

那我们可以直接查 最近 （也就是max）的时间 然后再做一个连接查询

这里由于时间相同的情况下会有不同数据，我们连表时再加一个查询最大id的子查询

修改后的sql:

SELECT scf.specode, scf.new_num AS ending_num, scf.new_price AS endingPrice, scf.new_fee AS endingFee

FROM (

SELECT specode, MAX(time) AS max_time

FROM sku_cost_flow

WHERE

time < UNIX_TIMESTAMP('2023-06-30 23:59:59')

AND specode IN (

...

)

GROUP BY specode

) scf_max

JOIN sku_cost_flow scf

ON scf.specode = scf_max.specode

AND scf.time = scf_max.max_time

AND scf.id = (

SELECT MAX(id)

FROM sku_cost_flow

WHERE specode = scf_max.specode

AND time = scf_max.max_time

)

优化结果：查询时间从一开始的7s -> 0.4s 扫描行数700w ->3w

如果有更好的方案，欢迎评论