rdlc report print barcode 3: Database Design in Visual Studio .NET

Encoder QR in Visual Studio .NET 3: Database Design

3: Database Design
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This form also eliminates repeating groups and attributes by putting each into a separate table and then connecting them with a PK and FK relationship Consider the following table used to build an invoice that does not comply with 1NF: OrderNumber (Primary key) CustomerName CustomerAddress Item1Name Item1Price Item1Qty Item2Name Item2Price Item2Qty This table has a couple of problems:
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It has columns that can be divided (CustomerName and CustomerAddress) It has repeating groups of items, prices, and quantities For a customer who wanted to purchase 3 items (or 303 items), the table wouldn t work
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The solution is to split the table into several related tables as shown in Figure 3-7 All nonkey fields in each table are dependent on the key
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Figure 3-7 Normalized tables to comply with 1NF
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2nd Normal Form (2NF)
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Second normal form (2NF) applies to tables that have composite primary keys, where two or more attributes comprise the PRIMARY KEY Every nonkey field needs to be dependent on the key A table is said to be in 2NF if it is in 1NF and every nonkey
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attribute is completely dependent on the whole primary key Consider the following OrderDetails table that does not comply with 2NF: OrderID (Primary key) ProductID (Primary key) Price Quantity SupplierAddress The problem with this table is that the SupplierAddress (the company that supplies this product to us so that we can sell it) is not dependent on the whole key (both the OrderID and ProductID) Instead, the SupplierAddress is dependent only on part of the PK (ProductID) One significant problem with this is that you d be forced to enter the SupplierAddress for every line entry on an order The solution would be to take SupplierAddress out of the OrderDetails table and put it into a separate table such as a Suppliers table It would then be referenced by the Product table using the PK of the Suppliers table - SupplierID The database diagram of the normalized tables would look similar to Figure 3-8
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Figure 3-8 Normalized table with SupplierAddress removed from OrderDetails table
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Note that we also broke up the SupplierAddress into the smaller parts (Street, City, Zip, and so on) to make it comply with 1NF
3rd Normal Form (3NF)
Third normal form (3NF) requires that there are no nontrivial functional dependencies of nonkey attributes on something other than the key In other words, fields within the table are only dependent on the PRIMARY KEY and are not dependent on nonkey fields Consider the following Parts table that does not comply with 3NF: PartNumber (Primary key) PartName PartDescription
3: Database Design
ManufacturerName ManufacturerAddress The problem is that the ManufacturerAddress is dependent on the ManufacturerName as much as it s dependent on the PartNumber Leaving it this way, we d have to repeat the data entry for the ManufacturerName and ManufacturerAddress for every single part In addition to cramped fingers, we d also get a fair share of typos where these are entered differently in different part numbers The solution would be to create a new table named Manufacturer, add the ManufacturerName column, columns for the address (street, city, state, zip), and reference that table with a PK and FK relationship on ManufacturerID The database diagram of the Parts and Manufacturer tables would look similar to Figure 3-9
Figure 3-9 A normalized database with the Manufacturer table added
Denormalization
While normalization of databases is an admirable goal, the truth is that we often denormalize a database for better performance That is, we selectively break some of the rules by adding redundant data A classic example of a database optimized with denormalization starts with a table similar to the following Product table: ProductID ProductName OnHandQty ProductPrice ProductCost For example, let s say that management is very interested in the cost value of onhand inventory and is requesting a report with this information on a daily basis We could query the Product table, and for every product in the table, we could multiply the quantity times the cost to give us an extended cost That s no big deal if you have only 200 products, but say you have 2 million products The calculation has to occur on each of the 2 million rows in the table each time the report is run To optimize the table for this query, we could denormalize it by adding another column named ExtendedCost We could use a script to populate the value of ExtendedCost in each row by multiplying ProductCost by OnHandQty To keep the data up to date, we could
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