Review 3 n 5

Review 3 n 5 - Chapter 3 1. Primary key is a key that is...

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1. Primary key is a key that is unique.That can determines other attributes in the same row. 2. Foreign key is an attribute that can be match with the primary key. The attribute is different from other attributes in the table. 3. Nulls happens when there is no data entry. Meaning the attribute has no data. A primary key cannot be null. 4. Composite key is a collection of more than one attribute. 5. Cardinality is the number of attributes in the row. Questions 1. What are the differences between unique index and index key? 2. What is the function of keys? Keys Each row in a table must be uniquely identifiable Key is one or more attributes that determine other attributes Key’s role is based on determination If you know the value of attribute A, you can determine the value of attribute B Functional independence: Attribute B functionally dependent on A if all rows in table that agree in value for A also agree in value for B 3. What are the relationship between data redundancy and anomalies? Data redundancy leads to data anomalies
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Review 3 n 5 - Chapter 3 1. Primary key is a key that is...

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