Checking when the SQL Instance started

Only for SQL 2008 an above, but this would be better:

 SELECT  sqlserver_start_time
 FROM    sys.dm_os_sys_info

EDIT:

I'm not sure how accurate the sys.dm_exec_requests version would be, what happens to that DMV if you drop clean buffers?

EDIT 2: Drop clean buffers doesn't change the entries of sys.dm_exec_requests , so that is my own myth busted! :)

p.s. don't test this assumption on a prod box. I didn't..... honest.....

I think it'll probably work. I'd call it an undocumented artifact and I wouldn't want to base major assumptions on it that affect my pay check or something like that, but yeah, I think it'll work.

I have compiled what is mentioned in this question and in this blog and run it on my machine:

 SELECT create_date FROM sys.databases WHERE name = 'tempdb'
 
 select start_time from sys.traces
 where is_default = 1
 
 SELECT login_time FROM sys.dm_exec_sessions
 WHERE session_id = 1;
 
 SELECT sqlserver_start_time FROM sys.dm_os_sys_info;
 
 EXEC sp_readerrorlog 0,1,'Copyright (c)'
 
 SELECT  MIN(start_time) as [Instance Started]
 FROM    [sys].[dm_exec_requests]

and

 NET STATISTICS SERVER

All give a slightly different result. I usually use the first and the last one.

Another way... and it won't work for everyone as some people use daily error logs etc.

 EXEC master.dbo.xp_readerrorlog 0, 1, 'Recovery is complete.', NULL, NULL, NULL, N'asc'

This basically returns when the system was ready.

Not a solution I would go with to base everything on but it does show that there are always alternatives :)

you can get instance startime by simply quering tempdb creation time.