-- DROP TABLE public.t_temperature

CREATE TABLE public.t_temperature (
	id int4 NOT NULL GENERATED ALWAYS AS IDENTITY,
	place_name varchar NOT NULL,
	value float8 NOT NULL,
	up_time timestamp NOT NULL,
	CONSTRAINT t_temperature_pk PRIMARY KEY (id)
);

-- Permissions

ALTER TABLE public.t_temperature OWNER TO postgres;
GRANT ALL ON TABLE public.t_temperature TO postgres;

INSERT INTO public.t_temperature (place_name,value,up_time) VALUES 
('广州',35,'2020-07-12 15:00:00.000')
,('广州',35.9,'2020-07-12 15:30:00.000')
,('深圳',30,'2020-07-12 15:30:00.000')
,('深圳',31,'2020-07-12 16:30:00.000')
,('三亚',23,'2020-07-12 16:30:00.000')
,('三亚',21,'2020-07-12 17:30:00.000')
,('北极',-1,'2020-07-12 17:30:00.000')
,('北极',-10,'2020-07-12 19:30:00.000')
;

select
	*
from
	(
	select
		tt.place_name,
		tt.value,
		tt.up_time,
		row_number() over ( partition by tt.place_name
	order by
		tt.up_time desc) as row_num
	from
		t_temperature tt) aaa
where
	aaa.row_num = 1

select
	dd.place_name,
	sum(case when dd.value <= 0 then 1 else 0 end) as 低温天气,
	sum(case when dd.value > 0 and dd.value < 25 then 1 else 0 end) as 正常天气,
	sum(case when dd.value >= 25 then 1 else 0 end) as 高温天气
from
	t_temperature dd
group by
	dd.place_name

select
	dd.place_name,
	sum(case when dd.value <= 0 then 1 else 0 end) as 低温天气,
	sum(case when dd.value > 0 and dd.value < 25 then 1 else 0 end) as 正常天气,
	sum(case when dd.value >= 25 then 1 else 0 end) as 高温天气
from
	(
	select
		*
	from
		(
		select
			tt.place_name,
			tt.value,
			tt.up_time,
			row_number() over ( partition by tt.place_name
		order by
			tt.up_time desc) as row_num
		from
			t_temperature tt) aaa
	where
		aaa.row_num = 1) dd
group by
	dd.place_name