Note in Figure 9-22 how LISTING and BID (Web server setup)
Note in Figure 9-22 how LISTING and BID tables can be merged into a single LISTING_BIDS table. Also, the two SELLER_HISTORY and BIDDER_HISTORY tables can be merged into a single HISTORY table. Figure 9-23 shows the resulting structure of a data warehouse database model for the online auction company. The data warehouse model shown in Figure 9-23 actually contains two star schemas. Figure 9-23: A data warehouse can have multiple star schemas (multiple fact tables, connected to the same dimensions). Seller Category Hierarchy Time Location Buyer Product Listing - Bids Seller Category Hierarchy Time Location Buyer Product History Data warehouse fact tables are relatively much larger than dimension tables (in record numbers). This is the objective of star schemas in making an efficient data warehouse database model. SQL code join queries between very small tables (dimensions with few records) and very large tables (facts with gazillions of records) are the most efficient types of joins. Joining two large tables, or even equally sized tables (assuming both tables contain more than thousands of records) is much less efficient. 247 Planning and Preparation Through Analysis
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