In which scenario do you have to manually adjust the database table after changing its definition?

When modifying a database table, particularly in a situation where data is already present, understanding how database tables react to changes is crucial. If a field is deleted from a table that contains data, it necessitates a manual adjustment for several reasons.

When a field is removed, not only does it affect the structure of the table, but it may also impact the integrity of the existing data, indexes, and queries that rely on that field. The database management system must ensure that all references to the deleted field are handled properly. This could involve adjustments to constraints, relationships, and dependent objects that interact with that field.

In scenarios where fields are added, like when a field is appended to a table containing data, the existing data remains unaltered, and the new field is simply added to the structure. Therefore, no manual adjustment is required because the integrity of the current data remains intact. Similarly, if a field is deleted from an empty table, there’s no existing data to conflict with, thus negating the need for manual intervention.

This highlights the importance of careful planning and execution when altering database table definitions, especially when data preservation and application integrity are at stake.