WHAT ARE INSERTION AND DELETION ANOMALIES?

Sumit Kesarwani

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Posted by  Sumit Kesarwani
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  1. Sumit Kesarwani

    Post:782

    Points:3910
    What are insertion and deletion anomalies?

    A deletion anomaly occurs when, by deleting the facts about one entity, we inadvertently delete facts about another entity; with one deletion, we lose facts about two entities. For example, if we delete the tuple for Student 001289 from a table, we may lose not only the fact that Student 001289 is in Pierce Hall, but also the fact that he has $200 left in his security deposit. An insertion anomaly happens when we encounter the restriction that we cannot insert a fact about one entity until we have an additional fact about another entity. For example, we want to store the fact that the security deposit for Pierce Hall is $300, but we cannot enter this data into the Student relation until a student registers for Pierce Hall.

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