How Compare two columns of Same SQL table to find duplicate records
You did not specify a particular RDBMS (SQL Server, Oracle, etc.), but here is a quick solution that would probably work on most.

Assuming your table has some kind of unique key (primary key - like ID) to determine the difference between one row and another row, you could use a correlated exists check.

SELECT a.*
FROM table1 a
WHERE EXISTS (
        SELECT *
        FROM table1
        WHERE StartDateTime = a.StartDateTime
            AND EndDateTime = a.EndDateTime
            AND Id &lt;&gt; a.Id
        )