Run query on each SQL Server instance - sql-server

Question

The first query retrieves the list of installed instances:
SET NOCOUNT ON
DECLARE #GetInstances TABLE
( Value nvarchar(100),
InstanceNames nvarchar(100),
Data nvarchar(100))
Insert into #GetInstances
EXECUTE xp_regread
#rootkey = 'HKEY_LOCAL_MACHINE',
#key = 'SOFTWARE\Microsoft\Microsoft SQL Server',
#value_name = 'InstalledInstances'
Select
InstanceNames
From
#GetInstances
SET NOCOUNT OFF
The second query could be anything but for the sake of argument, this one will do; it retrieves the list of trace ids for each trace instance:
select distinct
info.eventid
from
sys.traces as tr
cross apply sys.fn_trace_geteventinfo (tr.id) as info
So in summary, I want to feed the resultant instances from the first query into the second query so that I return all the values for all of the installed instances. There could be just one default instance but there could also be several.

Answer 1

Sounds like you could use a Cursor.
Note: Cursors are kinda slow, and generally you want to keep them to a minimum.
Check out this link to learn about them in depth.
But to be short: they can let you loop over a result set and execute tsql per row
Your code:
declare #GetInstances table
(
Value nvarchar(100),
InstanceNames nvarchar(100),
Data nvarchar(100)
)
insert into #GetInstances
exec xp_regread
#rootkey = 'HKEY_LOCAL_MACHINE',
#key = 'SOFTWARE\Microsoft\Microsoft SQL Server',
#value_name = 'InstalledInstances'
declare #Cursor as cursor;
declare #Server varchar(50);
set #Cursor = cursor for
select
InstanceNames
from
#GetInstances
open #Cursor;
fetch next from #Cursor into #Server;
while ##fetch_status = 0
begin
print #Server
fetch next from #Cursor into #Server;
END
close #Cursor;
deallocate #Cursor;
edit:
To use this server name to execute a proc, we need 2 things.
We need to make sure the server is setup as a linked server
We need to write a tiny bit of dynamic SQL (This is simple, don't worry)
Linked server
Linked servers are pretty simple in concept. Basically, they allow communication between severs via t-sql.
To setup a linked server, Microsoft has documentation here, but basically, in ssms, right click Server Objects > New > Linked Server and then follow all the steps to setup a sql server linked server.
And then boom. You now have a linked server.
Dynamic sql
Dynamic sql is cool and useful, and can really help in situations like this.
Normally, how we would execute a stored procedure on a linked server is this:
exec [RemoteServer].DatabaseName.Schema.StoredProcedureName
but, in our case, we don't know what [RemoteServer] is at time of writing. So what we can do, is write some Dynamic sql. With dynamic sql, what we can do is execute a string of tsql on our db, so we can do something like
exec(#Server + '.DatabaseName.Schema.StoredProcedureName')
and it runs the proc on the remote server.