TERADATA case when statement in WHERE clause - teradata

Question

I need to write a case statement in the WHERE clause, which is -
when current_date is 1st of Month then select data BETWEEN 1st day of prev month AND last day prev month
ELSE FROM 1st of Curr month till date. I have written this so far but it is not working. '05/01/2017' will be input date.
SELECT *
FROM MyTable
WHERE calendar_date
BETWEEN
CASE WHEN extract (day from CAST( '05/01/2017' AS DATE FORMAT 'MM/DD/YYYY')) =1 --check to see date is 1st of month
THEN ADD_MONTHS((CAST( '05/01/2017' AS DATE FORMAT 'MM/DD/YYYY') - EXTRACT(DAY FROM CAST( '05/01/2017' AS DATE FORMAT 'MM/DD/YYYY'))+1), -1) --1st of prev month
AND ADD_MONTHS(CURRENT_DATE - EXTRACT(DAY FROM CURRENT_date), 0 ) --last day prev month
ELSE CAST( '05/01/2017' AS DATE FORMAT 'MM/DD/YYYY') - EXTRACT(DAY FROM CAST( '05/01/2017' AS DATE FORMAT 'MM/DD/YYYY'))+1, 0) --else 1st of Curr mont
AND CURRENT_DATE
end
order by calendar_date

Answer 1

select *
from mytable
where calendar_date between case
when td_day_of_month (current_date) = 1
then current_date - interval '1' month
else td_month_begin (current_date)
end
and case
when td_day_of_month (current_date) = 1
then current_date - 1
else current_date
end
order by calendar_date

Answer 2

#Dudu, based on your suggestion, I was able to solve the sql. here it is:
SELECT * FROM MYTABLE
WHERE CALENDAR_DATE
BETWEEN
CASE WHEN extract (day from CAST( '05/15/2017' AS DATE FORMAT 'MM/DD/YYYY')) = 1
THEN (ADD_MONTHS((CAST( '05/15/2017' AS DATE FORMAT 'MM/DD/YYYY') - EXTRACT(DAY FROM CAST( '05/15/2017' AS DATE FORMAT 'MM/DD/YYYY'))+1), -1) )
ELSE ADD_MONTHS(CURRENT_DATE - EXTRACT(DAY FROM CURRENT_DATE)+1, 0)
END
AND
CASE WHEN extract (day from CAST( '05/15/2017' AS DATE FORMAT 'MM/DD/YYYY')) > 1
THEN CURRENT_DATE
ELSE ADD_MONTHS(CURRENT_DATE - EXTRACT(DAY FROM CURRENT_date), 0 )
END
AND REPORTNAME_MASTER_ID IN (2565,5216,5364)
order by CALENDAR_DATE