I want to have the result of a sql request between 2 dates with conditions

i have a problem with having the amount of a colomun1 in SQL. The user will enter 2 dates : Start date and end date in this format "YYYYMM". And i have to display the amount of the colomun1. If the column1 has changed value during the entered year YYYY (from January to December) (i.e : there are 2 values ​​in the database for the inserted year) I must display the "error" message otherwise display the value.