如何使用Tsql在varchar（6）中转换和计算日期时间类型yyyymm

Question

I have 2 columns with datatype varchar(6) like this, format yyyymm . Now I want to datediff between them. This is my solution,

select
    tblA, 
    tblB, 
    datediff(month, convert(datetime, tblA+'01', 120),convert(datetime, tblb+'01',120)+1 as count
from mytbl 

any other ideas? Thanks

Answer 1

It turns out that strings of the form YYYYMMDD can be converted directly to date values with no format needed. So, a slightly simpler version is:

select tblA, tblB, 
       datediff(month, convert(date, tblA + '01'), convert(datetime, tblb+'01')+1 as cnt
from mytbl;

I should note that you could also do:

select ( (left(tblA, 4) * 12 + right(tblA, 2)) - 
         (left(tblB, 4) * 12 + right(tblB, 2))
       )

SQL Server will convert the strings to numbers in a numeric context.

Also, I find it strange that date columns are called tblA and tblB , but that is how the question is phrased.

Answer 2

You can try this as well...

select dt1,dt2,
       datediff(month,concat(left(dt1, 4),'-',right(dt1, 2),'-01'),concat(left(dt2, 4),'-',right(dt2, 2),'-01')) dateDiff 
from mytbl