Q：现在有一张now表，如下图 想统计某个时间点上，situation字段为1、2、3、4数据条数各有多少？
A：新建视图，查询部分如下
select `now`.`time` AS `time`, sum((case when (`now`.`situation` = 1) then 1 else 0 end)) AS `proportion1`, sum((case when (`now`.`situation` = 2) then 1 else 0 end)) AS `proportion2`, sum((case when (`now`.`situation` = 3) then 1 else 0 end)) AS `proportion3`, sum((case when (`now`.`situation` = 4) then 1 else 0 end)) AS `proportion4` from `now` group by `now`.`time` order by `now`.`time`查询结果如下图：
