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SQL Relational Model Oracle Tips by Burleson Consulting High Performance Data Warehousing Introduction of the Relational Model Dr. Codd also introduced the concept of the Structured Query Language (SQL). One should note that SQL is not a query language; SQL performs much more than queries (SQL allows updates, deletes, and inserts). SQL is also not a language (SQL is embedded within procedural languages such as COBOL or C). Consequently, the name of Structured Query Language seemed a logical name for Dr. Codd's new tool. SQL offers three classes of operators: select, project, and join. The select operator serves to shrink the table vertically by eliminating unwanted rows (tuples). The project operator serves to shrink the table horizontally by removing unwanted columns. And the join operator allows the dynamic linking of two tables that share a common column value. Most commercial implementations of SQL do not support a project operation, and projections are achieved by specifying the columns desired in the output. The join operation is achieved by stating the selection criteria for two tables and equating them with their common columns. This is an excerpt from "High Performance Data Warehousing", copyright 1997. If you like Oracle tuning, you may enjoy the book Oracle Tuning: The Definitive Reference , with over 900 pages of BC's favorite tuning tips & scripts.  You can buy it directly from the publisher and save 30%, and get instant access to the code depot of Oracle tuning scripts.   ��

 

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