Error 15023: User already exists in current database. I fix it with sp_change_users_login, using Report, Auto_Fix or Update_One to link the user to a login.
SQL SERVER – Primary Key Constraints and Unique Key Constraints
Primary Key and Unique Key both enforce uniqueness, but they differ in the index they create and in NULL handling. Here are the differences and the scripts.
SQL SERVER – ReIndexing Database Tables and Statistics with Targeted Maintenance
ReIndexing Database tables starts with a measured maintenance need. I check the workload before choosing an index operation.