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Слайды и текст этой презентации

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Normalisation

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Success criteria know what is normalization know the purpose of the 3 forms of normalization (1NF, 2NF, 3NF) can create 3 forms of normalization for a table

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Database normalization is the process of removing redundant data from your tables in to improve storage efficiency, data integrity, and scalability. Database normalization is the process of removing redundant data from your tables in to improve storage efficiency, data integrity, and scalability. In the relational model, methods exist for quantifying how efficient a database is. These classifications are called normal forms (or NF), and there are algorithms for converting a given database between them.

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1NF - Atomic Data Test 1NF - Atomic Data Test If a table has a primary key it is said to be in First Normal form if the table does not have repeating groups of attributes. All attributes within the table need to be dependent only on the primary key. 2NF - Partial Dependence Test For a table to be in Second Normal form it must first be in First Normal (1NF) Form and then contain no data that is dependent on only part of the Primary Key 3NF - Non-Key Dependence Test For a table to be in Third Normal Form(3NF) it must be in Second Normal form and contain No data that is not dependent on the primary Key e.g. (Remove columns that are not dependent upon the primary key.)

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Take the following table. StudentID is the primary key.

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No. There are repeating groups (subject, subjectcost, grade)

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Create new rows so each cell contains only one value

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No – the studentID no longer uniquely identifies each row

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So. We now have 1NF.

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Studentname and address are dependent on studentID (which is part of the key) This is good.

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And 2NF requires…

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So it’s not 2NF

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Make new tables Make a new table for each primary key field Give each new table its own primary key Move columns from the original table to the new table that matches their primary key…