Need to pull a row if the Payment date is current month and Statement date is previous month: Teradata SQL

Question

I have a data like below:

Past_due_date.    statement_begin_date   statement_end_dt
2018-07-10          2018-04-11               2018-05-10
2018-07-10          2018-05-11               2018-06-10
2018-07-10          2018-06-11               2018-07-10
2018-07-10          2018-07-11               2018-08-10

I need to pull a record that has the previous month statement end date if the past_due_date is a current month like:

Past_due_date.    statement_begin_date   statement_end_dt
2018-07-10          2018-05-11               2018-06-10

I am currently using this function but its matching the record only for the current month ie YYYYMM of statement_ed_date = YYYYMM of past_due date, but i want something like, YYYYMM of past_due_dt= Statment_end_dt-1 month

CAST(cast(A.STMT_END_DT as date format 'YYYYMM') as CHAR(6))=CAST(cast(b.Past_due_fee_dt as date format 'YYYYMM') as CHAR(6)) 

Ps it doesnt have to be in YYYYMM format

Answer 1

Instead of converting to a string you better compare to the 1st of month:

where trunc(add_months(Past_due_fee_dt,-1), 'm') = trunc(STMT_END_DT, 'm') 

But to compare to the current & previous month you can simply calculate begin/end of the months:

where Past_due_fee_dt between trunc(current_date, 'm')               -- 1st day of current month
                          and last_day(current_date)                 -- last day of current month
  and STMT_END_DT between trunc(add_months(current_date, -1), 'm')   -- 1st day of previous month
                          and last_day(add_months(current_date, -1)) -- last day of previous month

Answer 2

I tried this and it worked for my case

CAST(cast(b.Past_due_fee_dt as date format 'YYYY') as VARCHAR(4))=CAST(cast(a.stmt_end_dt as date format 'YYYY') as VARCHAR(4)) and (CAST(cast(B.Past_due_fee_dt as date format 'MM') as VARCHAR(2))-CAST(cast(a.stmt_end_dt as date format 'MM') as VARCHAR(2)))=1