SQL Server：为前一个月设置两个变量，月份和年份，年份翻转安全

Question

I'm trying to basically dynamically set two variables (@month and @year) to be whatever the previous month and year were.

So in today's case @month = 7 and @year = 2012

But I want something safe for the year roll around, so if it's 1/1/2013 I would get @month = 12 and @year = 2012 .

Thanks!

This is what I have.

declare @month              int
declare @year               int

set @month = month (getDate ())-1
set @year = 2012

Answer 1

You can use DATEADD to subtract a month from the current date, then grab the MONTH and YEAR portions:

DECLARE @monthAgo dateTime
DECLARE @month int
DECLARE @year int

SET @monthAgo = DATEADD(month, -1, GETDATE())
SET @month = MONTH(@monthAgo)
SET @year = YEAR(@monthAgo)

Answer 2

Shown in steps. You can modify the value assigned to @Now to test.

DECLARE @Now DateTime = GETDATE();
DECLARE @Then DateTime = DATEADD(Month, -1, @Now);

DECLARE @Month Int = DATEPART(Month, @Then);
DECLARE @Year Int = DATEPART(Year, @Then);

SELECT @Month, @Year;

Answer 3

As a single query, this gives the first day of last month:

select DATEADD(month,DATEDIFF(month,'20010101',CURRENT_TIMESTAMP),'20001201')

You can, if you choose, pull that apart into two separate variables, but why bother? (I assume the rest of what you're doing is working with datetime s also, rather than int s)

---

The two datetime strings above are selected because they have the desired relationship between them - that the second starts 1 month before the first.

Answer 4

can you not just add, after what you already have:

if @month = 0
begin
  set @month = 12
  set @year = @year - 1
end

Answer 5

Try this

declare @month int
declare @year int
Declare @dt datetime=getdate()
set @month = DATEPART(mm,DATEADD(mm,-1,@dt))
select @month
set @year = DATEPART(yy,DATEADD(mm,-1,@dt))
select @year