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Oracle Tables, Columns and Views
Oracle Tips by Burleson
 

Data in an Oracle database resides in tables. A database typically contains many tables, each of which typically has many referential integrity links to other tables. There are two types of elements within tables: columns and rows.

A column is a single data element that contributes to the structure of a row. All tables must have at least one column; most have at least four or five columns. The maximum number of columns that can exist in a table is 255. Each column within the table is given a datatype.

A row is a group of related data elements in which each item of the group corresponds to a column. A table typically contains many rows. In large data warehouses, large tables may contain tens of millions of rows.

Views

A structure quite similar to a table is a view. Views are essential SQL queries stored in a database as an object. When a reference is made to the object, the query is executed and the result set is returned to the user. Figure 2.5 illustrates the relationship of a view to its base tables.

The use of views has serious performance implications. While the views makes SQL and PL/SQL code easier to develop and maintain, there is significant overhead involved (remember, views are essentially queries that execute when someone references the view).

Views are often used in systems when a certain functionality requires a complex join of tables. This is often the case when several tables must be joined to create the structure of the view, since the typical user doesn’t have the knowledge needed to join the tables effectively.


 

This is an excerpt from the book "High Performance Oracle Database Automation" by Jonathan Ingram and Donald K. Burleson, Series Editor.

  
 

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