query – How to find records based on a date range for other related data

I have below records in the table

APP_No Stage Start_Date End_Date
A123 L1 01-01-19 02-01-19
A123 D1 01-03-19 05-03-19
A345 L1 01-01-19 02-01-19
A345 D1 01-03-19 05-03-19

I want to search the D1 step records for the month of March19, but this must also include the data for step L1 as well, since the associated application IDs are between the same date range. I used the condition in the where clause in the following form: trunc (column_name) BETWEEN trunc (sysdate, mm) / current month / AND SYSDATE

Please help with the solution