The SQL statement below will give you the top 100 longest running SQL statements in your database, sorted by duration.
SELECT TOP 100 qs.total_elapsed_time / qs.execution_count / 1000000.0 AS average_seconds, qs.total_elapsed_time / 1000000.0 AS total_seconds, qs.execution_count, SUBSTRING (qt.text,qs.statement_start_offset/2, (CASE WHEN qs.statement_end_offset = -1 THEN LEN(CONVERT(NVARCHAR(MAX), qt.text)) * 2 ELSE qs.statement_end_offset END - qs.statement_start_offset)/2) AS individual_query, o.name AS object_name, DB_NAME(qt.dbid) AS database_name FROM sys.dm_exec_query_stats qs CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) as qt LEFT OUTER JOIN sys.objects o ON qt.objectid = o.object_id where qt.dbid = DB_ID() ORDER BY average_seconds DESC;