Candidate key
A candidate key is a minimal set of attributes whose values uniquely identify each row in a relational relation.
100 SQL Server Mistakes and How to Avoid Them
A candidate key is a minimal set of attributes that uniquely identifies every row in a relation.
- How it is used
- Uses candidate keys to ensure unique rows while preparing relations for first normal form.
- How deep it goes
- Defines super keys, minimality, single-attribute keys, and composite keys through relation examples.
- Examples
- Contrasts Sales Order Number, Purchase Order Number, and the Product Name plus Product Type Name pair.
- What you can do after
- Evaluate/understand whether one attribute or a minimal attribute combination uniquely identifies relation rows.
Read how 100 SQL Server Mistakes and How to Avoid Them explains candidate key →
Grokking Relational Database Design
A minimal combination of table attributes whose values uniquely identify a row, with no removable attribute retaining that property.
- How it is used
- Guides selection of a primary key while designing entities and preparing tables for normalization.
- How deep it goes
- Defines minimal superkeys, contrasts them with superkeys and primary keys, and demonstrates minimality with a user-table combination.
- Examples
- Uses unique username, email, and phone_number values, plus the nonminimal username and first_name combination.
- What you can do after
- Evaluate/understand whether attributes uniquely identify rows without unnecessary columns and choose a primary-key candidate.
Read how Grokking Relational Database Design explains candidate key →
Related concepts
- superkeykind of · A superkey is a set of one or more attributes whose values uniquely identify each row in a relation, whether or not the set is minimal.
- primary keyincludes · 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.
- natural keyincludes · A natural key is an identifier formed from meaningful domain attributes whose values uniquely identify an entity or record.
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