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Functional Dependencies
If a column's value is determined by one or more other columns, then that forms a functional dependency.
| employee_name | department_id | department_name |
|---|---|---|
| Lane | 10 | Accounting |
| Daniel | 10 | Accounting |
| Allan | 20 | Marketing |
Here, department_id determines department_name. The data that "department 10 is Accounting" is duplicated in the first and second rows. This data redundancy is why data normalization cares about dependencies between columns.