User and login mapping after an SQL Server restore

Question

I need to restore a DB from an SQL Server instance to another and I am well aware that the DB users will be transferred but the logins won't. I have created a script to be able to create the logins on the destination SQL Server instance, including the password hashed and the login SID. However, I am uncertain if it makes a difference whether the logins are created on the destination instance prior to the DB restore or after the DB is restored.

If the logins are created first and then the DB is restored, the DB users will map with the existing corresponding logins accordingly due to SID, however, if I do the DB restore and create the logins afterwards, will they still map automatically or will one need to do an ALTER USER WITH LOGIN or similar?

Answer 1

I completely agree with Tony Hinkle that it doesn't matter when the logins are created i.e. either before or after restoration. If you create logins after restoration, during that interval those users will be orphan users since they don't have their corresponding login(SID) in the server. You should also be careful on the system created users(NT Users) and their SIDs.

You may refer below script for easy transfer of logins form one server to another server:

USE master
GO
IF OBJECT_ID ('sp_hexadecimal') IS NOT NULL
 DROP PROCEDURE sp_hexadecimal
GO
CREATE PROCEDURE sp_hexadecimal
 @binvalue varbinary(256),
 @hexvalue varchar (514) OUTPUT
AS
DECLARE @charvalue varchar (514)
DECLARE @i int
DECLARE @length int
DECLARE @hexstring char(16)
SELECT @charvalue = '0x'
SELECT @i = 1
SELECT @length = DATALENGTH (@binvalue)
SELECT @hexstring = '0123456789ABCDEF'
WHILE (@i <= @length)
BEGIN
 DECLARE @tempint int
 DECLARE @firstint int
 DECLARE @secondint int
 SELECT @tempint = CONVERT(int, SUBSTRING(@binvalue,@i,1))
 SELECT @firstint = FLOOR(@tempint/16)
 SELECT @secondint = @tempint - (@firstint*16)
 SELECT @charvalue = @charvalue +
 SUBSTRING(@hexstring, @firstint+1, 1) +
 SUBSTRING(@hexstring, @secondint+1, 1)
 SELECT @i = @i + 1
END
SELECT @hexvalue = @charvalue
GO
IF OBJECT_ID ('sp_help_revlogin') IS NOT NULL
 DROP PROCEDURE sp_help_revlogin
GO
CREATE PROCEDURE sp_help_revlogin @login_name sysname = NULL AS
DECLARE @name sysname
DECLARE @type varchar (1)
DECLARE @hasaccess int
DECLARE @denylogin int
DECLARE @is_disabled int
DECLARE @PWD_varbinary varbinary (256)
DECLARE @PWD_string varchar (514)
DECLARE @SID_varbinary varbinary (85)
DECLARE @SID_string varchar (514)
DECLARE @tmpstr varchar (1024)
DECLARE @is_policy_checked varchar (3)
DECLARE @is_expiration_checked varchar (3)
DECLARE @defaultdb sysname
IF (@login_name IS NULL)
 DECLARE login_curs CURSOR FOR
 SELECT p.sid, p.name, p.type, p.is_disabled, p.default_database_name, l.hasaccess, l.denylogin FROM 
sys.server_principals p LEFT JOIN sys.syslogins l
 ON ( l.name = p.name ) WHERE p.type IN ( 'S', 'G', 'U' ) AND p.name <> 'sa'
ELSE
 DECLARE login_curs CURSOR FOR
 SELECT p.sid, p.name, p.type, p.is_disabled, p.default_database_name, l.hasaccess, l.denylogin FROM 
sys.server_principals p LEFT JOIN sys.syslogins l
 ON ( l.name = p.name ) WHERE p.type IN ( 'S', 'G', 'U' ) AND p.name = @login_name
OPEN login_curs
FETCH NEXT FROM login_curs INTO @SID_varbinary, @name, @type, @is_disabled, @defaultdb, @hasaccess, @denylogin
IF (@@fetch_status = -1)
BEGIN
 PRINT 'No login(s) found.'
 CLOSE login_curs
 DEALLOCATE login_curs
 RETURN -1
END
SET @tmpstr = '/* sp_help_revlogin script '
PRINT @tmpstr
SET @tmpstr = '** Generated ' + CONVERT (varchar, GETDATE()) + ' on ' + @@SERVERNAME + ' */'
PRINT @tmpstr
PRINT ''
WHILE (@@fetch_status <> -1)
BEGIN
 IF (@@fetch_status <> -2)
 BEGIN
 PRINT ''
 SET @tmpstr = '-- Login: ' + @name
 PRINT @tmpstr
 IF (@type IN ( 'G', 'U'))
 BEGIN -- NT authenticated account/group
 SET @tmpstr = 'CREATE LOGIN ' + QUOTENAME( @name ) + ' FROM WINDOWS WITH DEFAULT_DATABASE = [' + @defaultdb + ']'
 END
 ELSE BEGIN -- SQL Server authentication
 -- obtain password and sid
 SET @PWD_varbinary = CAST( LOGINPROPERTY( @name, 'PasswordHash' ) AS varbinary (256) )
 EXEC sp_hexadecimal @PWD_varbinary, @PWD_string OUT
 EXEC sp_hexadecimal @SID_varbinary,@SID_string OUT
 -- obtain password policy state
 SELECT @is_policy_checked = CASE is_policy_checked WHEN 1 THEN 'ON' WHEN 0 THEN 'OFF' ELSE NULL END FROM sys.sql_logins WHERE name = @name
 SELECT @is_expiration_checked = CASE is_expiration_checked WHEN 1 THEN 'ON' WHEN 0 THEN 'OFF' ELSE NULL END FROM sys.sql_logins WHERE name = @name
 SET @tmpstr = 'CREATE LOGIN ' + QUOTENAME( @name ) + ' WITH PASSWORD = ' + @PWD_string + ' HASHED, SID = ' + @SID_string + ', DEFAULT_DATABASE = [' + @defaultdb + ']'
 IF ( @is_policy_checked IS NOT NULL )
 BEGIN
 SET @tmpstr = @tmpstr + ', CHECK_POLICY = ' + @is_policy_checked
 END
 IF ( @is_expiration_checked IS NOT NULL )
 BEGIN
 SET @tmpstr = @tmpstr + ', CHECK_EXPIRATION = ' + @is_expiration_checked
 END
 END
 IF (@denylogin = 1)
 BEGIN -- login is denied access
 SET @tmpstr = @tmpstr + '; DENY CONNECT SQL TO ' + QUOTENAME( @name )
 END
 ELSE IF (@hasaccess = 0)
 BEGIN -- login exists but does not have access
 SET @tmpstr = @tmpstr + '; REVOKE CONNECT SQL TO ' + QUOTENAME( @name )
 END
 IF (@is_disabled = 1)
 BEGIN -- login is disabled
 SET @tmpstr = @tmpstr + '; ALTER LOGIN ' + QUOTENAME( @name ) + ' DISABLE'
 END
 PRINT @tmpstr
 END
 FETCH NEXT FROM login_curs INTO @SID_varbinary, @name, @type, @is_disabled, @defaultdb, @hasaccess, @denylogin
 END
CLOSE login_curs
DEALLOCATE login_curs
RETURN 0
GO

Please note that you need to cross check for these logins for their permissions.

• mprost: In case somebody is wondering, this is the source of that script: learn.microsoft.com/en-US/troubleshoot/sql/database-engine/…

Answer 2

It doesn't matter when the logins are created. As long as the SIDs match, the database user will be associated with the login.

Every time a user attempts to connect to a database, SQL Server is going to check for a mapped login (unless it's a contained database). It does this by checking to see if there is a login with a SID that matches the user's SID. Accordingly, it doesn't matter when the login was created because it will be matched at the the time the user attempts to connect to the database.