Msg 15138 - The database principal owns a schema in the database and cannot be dropped.

Question: I’ve attempted to drop a SQL Server database user. When I execute the  DROP USER , I receive the error message:

Msg 15138, Level 16, State 1, Line 2

The database principal owns a schema in the database, and cannot be dropped.

How can I fix this problem?

Answer:

Step 1 : Find out the database schemas owned by the database user

SELECT name FROM  sys.schemas WHERE principal_id = USER_ID(a_user_id)

Step 2 : Either drop the schema or change the schema owner

To drop the database schema

DROP SCHEMA [my_schema_name]

You may receive an error message  such as :

Cannot drop schema 'my_schema_name' because it is being referenced by object 'a_table'.

Investigate and decide on how you want to handle the objects within the schema. 

To change the schema owner

ALTER AUTHORIZATION ON SCHEMA::my_schema_name TO dbo

Step 3: Drop the SQL Server database user

DROP USER myUser

It's advisable to generate a backup or generate a script of the user status BEFORE you make any changes. 

Read more on managing SQL Server database security