[DMV] Slowest queries

Here is example to find which query is the slowest query in my db. 

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED SELECT TOP 20 CAST(qs.total_elapsed_time / 1000000.0 AS DECIMAL(28, 2)) AS [Total Elapsed Duration (s)] , qs.execution_count , SUBSTRING (qt.text,(qs.statement_start_offset/2) + 1, ((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) + 1) AS [Individual Query] , qt.text AS [Parent Query] , DB_NAME(qt.dbid) AS DatabaseName , qp.query_plan FROM sys.dm_exec_query_stats qs CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) qt CROSS APPLY sys.dm_exec_query_plan(qs.plan_handle) qp ORDER BY total_elapsed_time DESC

This is the result of my db.