（013）每日SQL学习：确定两个日期之间的工作日天数和计算一年周内各日期次数

--确定两个日期之间的工作日天数
with x0 as 
(select to_date(‘2018-01-01‘,‘yyyy-mm-dd‘) as 日期 from dual
union all
select to_date(‘2018-01-15‘,‘yyyy-mm-dd‘) as 日期 from dual ),
x1 as --日期并列显示 
(select min (日期) 开始日期,max(日期) 结束日期 from x0 ),
x2 as --日期之间的天数
(select 结束日期-开始日期+1  as 天数 ,开始日期,结束日期 from x1),
x3 as --构造一个从开始日期到结束日期的日期集合 （枚举日期）
(select to_char(开始日期+level-1,‘DY‘) as 枚举日期 from x2 connect by level <=天数)
--统计日期
select sum(case when 枚举日期 in (‘sat‘,‘sun‘)then 0 else 1 end ) as 工作日 from x3

--计算一年周内各日期次数
with x0 as 
(select to_date(‘2018-01-01‘,‘yyyy-mm-dd‘) as 年初 from dual ),
x1 as 
(select 年初,add_months(年初,12) as 下年年初 from x0),
x2 as 
(select 年初,下年年初,下年年初-年初 as 天数  from x1),
x3 as 
(select 年初+level-1 as 日期 from x2  connect by level <=天数 ),
x4 as 
(select 日期,to_char(日期,‘DAY‘) AS 星期 FROM X3)

SELECT 星期,count(*) from x4 group by 星期

with x0 as 
(select ‘1‘as name ,to_date(‘2018-01-01‘,‘yyyy-mm-dd‘) as 日期 from dual
union all
select ‘2‘ as name,to_date(‘2018-01-15‘,‘yyyy-mm-dd‘) as 日期 from dual
union all
select ‘3‘ as name, to_date(‘2018-01-26‘,‘yyyy-mm-dd‘) as 日期 from dual )

select 
name ,日期,next_d,(next_d-日期) as 相差天数
 from (
      select name ,日期,
      lead(日期,1,null) over (order by 日期) as next_d
      from x0
)