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A Model for SQL

Oracle Tips by Burleson Consulting

The first model of SQL can be thought of as having three categories of function: Define, Manipulate, and Authorize.

  • Define refers to the data definition language (DDL) that performs object create, drop, and alter functions.
  • Manipulate refers to the data manipulation language (DML) that performs select, insert, update, and delete functions.
  • Authorize refers to the control that performs grant and revoke functions.

Within the Manipulate functions, we see three dimensions to SQL, select, project, and join. These three simple metrics define the whole functionality of SQL.

Select Operation

A select operation reduces the length of a table by filtering out unwanted rows. By specifying conditions in the where clause, the user can filter unwanted rows out of the result set, as shown in Figure 1-2. In sum, the select operation reduces the results vertically.

Figure 2: A select filter reduces the number of returned rows

Project Operation

Just as the select operation reduces the number of rows, the project operation reduces the number of columns. The column names specified in the SQL select determine those columns that are displayed, as shown in Figure 1-3. In sum, the project operation reduces the size of the result set horizontally.

Figure 3: The project operation removes unwanted columns

Join Operation

A join operation such as is shown in Figure 1-4 is used to relate two or more independent tables that share a common column. In a join, two or more independent tables are merged according to a common column value.

Figure 4: A join operation

Within this simple framework we see that a query in SQL is a “state-space” type of query. That is, the person who writes the query does not need to be concerned with the navigation path to the data. The SQL optimizer handles the navigation path to the data tables internally.

 

This is an excerpt from "Oracle High-Performance SQL Tuning" by Donald K. Burleson, published by Oracle Press.


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