Varchar operation in SQL 2014

Question

I am trying to do a less sql account in sql Sever management but this format error. I am wanting to do the months account 202103 - 202101 = 2 months

How to solve this format problem?

select *
    ,DPD = datediff(day, Dt_Atraso, Dt_Ref)
    ,DIAS_Prazo = datediff(day, Dt_Abertura, Dt_Vencimento)
    **,DIFERENCA = (MES_ATUAL - MES_ATRASO)**
from #chuv_pJ 

ERROR:

Msg 402, Level 16, State 1, Line 4
The data types varchar and varchar are incompatible in the subtract operator.

Answer 1

The problem is that it is trying to subtract two varchar-like fields. It will be necessary to make a cast before. That cast will consider the value as date in order to be able to perform the calculation between dates. Before performing the cast, I suggest concatenating with the string +'01' to generate a valid date as per functional example below:

    select *
        ,DPD = datediff(day, Dt_Atraso, Dt_Ref)
        ,DIAS_Prazo = datediff(day, Dt_Abertura, Dt_Vencimento)
        ,DIFERENCA = DATEDIFF(MONTH,cast(MES_ATRASO+'01' as date),cast(MES_ATUAL+'01' as date))
    from #chuv_pJ 

Answer 2

As suggested in comment, to have the difference between two dates in months, you just need to change the "datepart", which is the first function parameter datediff().

SELECT *,
    DPD = datediff(day, Dt_Atraso, Dt_Ref),
    DIAS_Prazo = datediff(day, Dt_Abertura, Dt_Vencimento),
    DIFERENCA = datediff(month, Dt_Abertura, Dt_Vencimento)
FROM #chuv_pJ