Functional dependency
A functional dependency is a relational constraint in which one set of attributes uniquely determines the values of another set of attributes.
100 SQL Server Mistakes and How to Avoid Them
A functional dependency is a relationship in which one set of attributes determines the value of another set of attributes.
- How it is used
- Uses functional dependency to test relations while moving a schema from 1NF to 2NF and 3NF.
- How deep it goes
- Explains partial and transitive dependencies through schema changes, without formal dependency notation or algorithms.
- Examples
- Uses Product Type Name and Product Type Description to expose a partial dependency.
- What you can do after
- Apply 2NF and 3NF checks by separating attributes determined by only part of a key or by nonprime attributes.
Read how 100 SQL Server Mistakes and How to Avoid Them explains functional dependency →
Grokking Relational Database Design
A functional dependency is a constraint in which a value or set of values in one or more columns uniquely determines the value of another column.
- How it is used
- Uses column-determination rules to normalize tables and check BCNF and 3NF designs.
- How deep it goes
- Explains direction, single-column and composite dependencies, and transitive chains, then stops short of edge cases.
- Examples
- Uses employee, purchase, product, supplier, department, and purchase_product tables to demonstrate dependencies and decomposition.
- What you can do after
- Apply it via normalization by locating wrongly dependent columns and moving them into appropriately keyed tables.
Read how Grokking Relational Database Design explains functional dependency →
Related concepts
- Boyce-Codd normal formused by · Boyce-Codd normal form is a relational normalization condition requiring every nontrivial functional dependency to have a superkey as its determinant.
- primary keyused by · A primary key is a designated column or attribute, or combination of them, that uniquely identifies each row or item in a table or data store.
- dependencykind of · A software dependency is a component, resource, or prerequisite on which another software component or operation relies to function or proceed.
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