How do I resolve the SQL server error 15151? As part of our server management services, Skynats provides answers to all of your questions.
SQL server error 15151
A login is a security principal or object that can be authenticated by a secure system. Users must log in to connect to SQL Server. You can make a login that is based on a Windows principal, like a domain user or a Windows domain group, or you can make one that is not (such as an SQL Server login).
A database security principle is a user. It is necessary to map logins to database users to connect to a database. A login can only map as one user in each database, even though it can map to various databases as different users. In a database that is only partially contained, a user without a login can be created. When a database’s guest user is enabled, a login that doesn’t map to a database user can access the database as the visitor user.
Database users are different from logins. Mapping Windows groups or logins to database users or roles must be done separately. The next step is to grant users or roles access to view database items.
Case 1
Error:
Msg 15151, Level 16, State 1, Line 2
Cannot alter the login ‘sa’, because it does not exist or you do not have permission.
Solution:
The absence of rights led to this error. The highest level of user in the system is designated by the abbreviation SA, or system administrator. A user must have greater or equivalent rights to the SA user to modify SA’s permissions.
Changes to the SA user’s rights can only be made by members of the systemadmin group. We can resolve the issue by first adding any user to the systemadmin role and then using the same account to change the system admin’s tool.
Case 2
Error:
Msg 15151, Cannot alter the user ‘xxxx’, because it does not exist or you do not have permission
Solution:
Before attempting to change the user, we must create it (CREATE USER [xxxx]). The error might be visible if the “create user” instruction is missing before the alter. Both the User and Login receive user access to a specific database on the server. Therefore, we must include create user from login in the script.
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