postgresql 日期处理函数用法

postgresql 日期处理函数用法

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select now(); --当前时间 2021-04-21 11:36:56

SELECT EXTRACT (year FROM now()); --年 2021

SELECT EXTRACT (quarter FROM now()); --季 02

SELECT EXTRACT (month FROM now()); --月 04

SELECT EXTRACT (day FROM now()); --月中天 21

SELECT EXTRACT (week FROM now()); --周 16

SELECT EXTRACT (isodow FROM now()); --周中天 3

SELECT EXTRACT (hour FROM now()); --時 11

SELECT EXTRACT (minute FROM now()); --分 36

SELECT EXTRACT (second FROM now()); --秒 56.909161

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获取年份：extract(year from 日期)
获取月份：extract(month from 日期)
获取季度：extract(quarter from 日期)

select
 months 月份,max(最高气温)最高温, min(最低气温)最低温, max(温差) 温差
from (
  select (extract(year from 日期)||'-'||extract(month from 日期)) as  months, 最高气温, 最低气温, 最高气温-最低气温 温差 
	from weather
  where extract(year from 日期) = '2018'
  ) a group by a.months order by months

postgresql 测试数据 别名要加as
mysql 要跟from dual
postgresql 则不跟dual

select 2 as id,'技术' as name, 2000 as value, '' as parent 
union
select 1 as id,'销售' as name, 5000 as value, '' as parent 
union
select 3 as id,'电话销售' as name, 2000 as value, '1' as parent 
union
select 4 as id,'门店销售' as name, 3000 as value, '1' as parent 
union
select 5 as id,'促销' as name, 2000 as value, '4' as parent 

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select 
'武侯区' as name, 123 as value
union
select
'青羊区' as name, 223 as value
union
select
'金牛区' as name, 453 as value
union
select
'双流区' as name, 423 as value
union
select
'新都区' as name, 163 as value
union
select
'郫都区' as name, 193 as value
union
select
'温江区' as name, 343 as value
union
select
'青白江区' as name, 443 as value
union
select
'锦江区' as name, 403 as value
union
select
'成华区' as name, 553 as value
union
select
'双流区' as name, 553 as value
union
select
'成都市' as name, 489 as value
union
select
'四川省' as name, 500 as value
union
select
'广东省' as name, 200 as value
union
select
'新疆维吾尔自治区' as name, 1000 as value
union
select
'青海省' as name, 900 as value
union
select
'西藏自治区' as name, 900 as value

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