Final answer:
To enforce a rule that one field value must be greater than another within the same table, use constraints, specifically a check constraint. Grouping data in tables depends on database design needs and data access patterns. Modifications in table structures are made to optimize performance and data integrity.
Step-by-step explanation:
If you require the value in one field of a table to always be greater than the value in another field within the same table, you would use constraints. A constraint is a rule that is applied to a column or a set of columns in a database table to limit the kind of data that can be stored in that column or columns. To ensure that one column's value remains greater than another's, you would typically use a check constraint to define this rule. This check constraint will be enforced by the database system at the time of inserting or updating records and will prevent any violations of the defined relationship between the two fields.
In general, when grouping data in tables, it could be advantageous to group related data close together or to normalize the data by separating it into different tables to prevent redundancy and improve data integrity. The choice of one method over the other would depend on the specific needs of your database design and the access patterns that you anticipate for your database.
Changing between tables or modifying the schema often occurs to improve performance, achieve more efficient data storage, or to ensure that business logic is consistently enforced, which can occasionally necessitate switching between different table structures or designs.