SQL Server: How to SELECT the installation path?

Question

i know there is a variable, function, or stored procedure that you can use to find the path that SQL Server is installed to:

e.g.:

c:\Program Files\Microsoft SQL Server\MSSQL.7\MSSQL

or

m:\CustomInstance\MSSQL

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In reality, i'm hoping to SELECT for the default backup path. But since i doubt that exists, i'll just tack \BACKUP onto the install path and call it close enough.

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Update One

select filename from sysaltfiles
where name = db_name()

Server: Msg 208, Level 16, State 1, Line 1
Invalid object name 'sysaltfiles'.

---

select filename from master.dbo.sysaltfiles
where name = db_name()

filename
---------------- 

(0 row(s) affected)

Answer 1

How to select the installation path

Note: xp_instance_regread doesn't read the registry key you specify, but instead converts that key path into the appropriate path for the specific SQL Server instance you're running on. In other words: xp_regread fails where xp_instance_regread succeeds.

SQL Server Installation Directory

declare @rc int, @dir nvarchar(4000) 

exec @rc = master.dbo.xp_instance_regread
      N'HKEY_LOCAL_MACHINE',
      N'Software\Microsoft\MSSQLServer\Setup',
      N'SQLPath', 
      @dir output, 'no_output'
select @dir AS InstallationDirectory

SQL Server Backup Directory

declare @rc int, @dir nvarchar(4000) 

exec @rc = master.dbo.xp_instance_regread
      N'HKEY_LOCAL_MACHINE',
      N'Software\Microsoft\MSSQLServer\MSSQLServer',
      N'BackupDirectory', 
      @dir output, 'no_output'
select @dir AS BackupDirectory

SQL Server 2000 Location Functions

Answer 2

Execute the following to inspect the registry in order to find the appropriate key.

Declare @Path as varchar(100);
Set @Path = NULL

Exec master..xp_regread 'HKEY_LOCAL_MACHINE', 'SOFTWARE\Microsoft\Microsoft SQL Server\70\Tools\ClientSetup', 'SQLPath', @Path OUTPUT
Select @Path as [Sql Server 7.0 path] 

Set @Path = NULL
Exec master..xp_regread 'HKEY_LOCAL_MACHINE', 'SOFTWARE\Microsoft\Microsoft SQL Server\80\Tools\ClientSetup', 'SQLPath', @Path OUTPUT
Select @Path as [Sql Server 2000 path] 

Set @Path = NULL
Exec master..xp_regread 'HKEY_LOCAL_MACHINE', 'SOFTWARE\Microsoft\Microsoft SQL Server\90\Tools\ClientSetup', 'SQLPath', @Path OUTPUT
Select @Path as [Sql Server 2005 path]

Set @Path = NULL
Exec master..xp_regread 'HKEY_LOCAL_MACHINE', 'SOFTWARE\Microsoft\Microsoft SQL Server\100\Tools\ClientSetup', 'SQLPath', @Path OUTPUT
Select @Path as [Sql Server KATMAI path]