Database refactoring does not change the way data is interpreted or used and does not fix bugs or add new functionality.
Every refactoring to a database leaves the system in a working state, thus not causing maintenance lags, provided the meaningful data exists in the production environment.
Methods of Data Quality Refactoring category: Add Lookup Table; Apply Standard Codes; Apply Standard Type; Consolidate Key Strategy; Drop Column Constraint; Drop Default Value; Drop Non Nullable; Introduce Column Constraint; Introduce Common Format; Introduce Default Value; Make Column Non Nullable; Move Data; Replace Type Code With Property Flags.
Methods of Referential Integrity Refactoring category: Add Foreign Key Constraint; Add Trigger for Calculated Column; Drop Foreign Key Constraint; Introduce Cascading Delete; Introduce Hard Delete; Introduce Soft Delete; Introduce Trigger for History.
In 2019 Vladislav Struzik supplemented the categories of database refactoring with a new one:[3] Methods of the Access Refactoring category:[4][5] Change Authentication Attributes; Revoke Authorization Privileges; Grant Authorization Privileges; Extract Database Schema; Merge Database Schemas.