Slow and long running queries

Famous query to show which queries are the worst performers.

SELECT TOP 50 creation_time
        ,last_execution_time
        ,total_physical_reads
        ,total_logical_reads
        ,total_logical_writes
        , execution_count
        , total_worker_time
        , total_elapsed_time
        , total_elapsed_time / execution_count avg_elapsed_time
        ,SUBSTRING(st.text, (qs.statement_start_offset/2) + 1,
         ((CASE statement_end_offset
          WHEN -1 THEN DATALENGTH(st.text)
          ELSE qs.statement_end_offset END
            - qs.statement_start_offset)/2) + 1) AS statement_text
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) st
where last_execution_time > '18 Feb 2016'
ORDER BY total_elapsed_time / execution_count DESC;

You may want to change the Order by...

You may lack permissions to run this. Specifically:

VIEW SERVER STATE permission was denied on object 'server', database 'master'.

Which requires this to be executed:

use master
go
GRANT VIEW SERVER STATE TO <user_name>

...if possible.