Data SQL select project join Oracle Tips  by Burleson Consulting

High Performance Data Warehousing

Introduction of the Relational Model

The following example incorporates a select, a project, and a join:

select cust_name, order_date /* PROJECT (choose columns) */
from CUSTOMER, ORDER
where
SEE CODE DEPOT FOR FULL SCRIPT

Due to its flexible nature, relational database are still the vehicle of choice for very large data warehouses. Unlike previous architectures, where all data relationships had to be hard-linked with pointers, the relational database allows for new data relationships to be added at any time with no changes to the physical database structure. All that is required is two tables with common key values, and the data relationship is established with a relational join. The relational model is also desirable for data warehouses because of the simplicity of SQL queries (at least, when compared to earlier data access methods). SQL for data retrieval has allowed for end user query tools to be developed where a non-computer professional can state the data that they need, and the tools generate the SQL on behalf of the end user. Because many data warehouse queries are ad hoc in nature, this is a very powerful feature.

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This is an excerpt from "High Performance Data Warehousing", copyright 1997.

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