Pattern: On First Calendar Day of Month, Filter Table for All Entries from Last Month
If you have a table containing rows with dates in a YYYY-MM-DD format, you can use this pattern to filter that table for all of last month's entries. This will require that you create a scheduled trigger, and run this once each day. The first actions get today's date, and then format it in a D format, i.e. 2020-07-28 would come back simply as 28.
The next action conditionally starts if today is the 1st calendar day of the month. If the workflow started on 2020-08-01, it allows you to construct advanced filter criteria for the Tables: Apply filters action. We can construct the below filter in an automated way:
columns['Your Date Here'] >= 2020-07-01 && columns['Your Date Here'] <= 2020-07-31
The datestamps 2020-07-01 and 2020-07-31 will always be dynamic. You'll need to update the data table ID in the Filter table for entries between first and last date of last month step.