MySQL高级函数case的使用技巧----与sum结合实现分段统计

1 CASE 
2     WHEN condition1 THEN result1
3     WHEN condition2 THEN result2
4    ...
5     WHEN conditionN THEN resultN
6     ELSE result
7 END

1 select
2      sum(case when b.device_id is not null then 1 else 0 end)  hasDeviceCount,
3      sum(case when b.detector_id is not null then 1 else 0 end) hasDetectorCount,
4      sum(case when b.status = 1 then 1 else 0 end)  hasOccupiedCount
5  from berth_info b;