Questions[SQL]：Calculate the Number of Days in a Month

Q：Can you use a batch SQL or store procedure to calculating the Number of Days in a Month?

A:

解法一：使用CTE，结构清晰

with arg0 as

(

--计算当月第一天

select cast(

cast(year(getdate()) as varchar)+'-'+cast(month(getdate()) as varchar)+'-01'

as datetime) as nowdt

),

arg1 as

(

--计算下月第一天

select dateadd(mm,1,nowdt) as dt from arg0

),

arg2 as

(

--计算下月减1，即本月最后一天

select dateadd(dd,-1, dt) as dt from arg1

),

arg3 as

(

--取天数部分

select datepart(dd, dt) as daies from arg2

)

select * from arg3

解法二：使用变量

declare @now datetime

set @now= cast(

cast(year(getdate()) as varchar)+'-'+cast(month(getdate()) as varchar)+'-01'

as datetime)

declare @day int

set @day = datepart(dd, dateadd(dd,-1, dateadd(mm,1,@now)))

select @day

解法三：单一语句

select datepart(dd,dateadd(dd,-1,dateadd(mm,1,cast(cast(year(getdate()) as varchar)+'-'+cast(month(getdate()) as varchar)+'-01' as datetime))));