Oracle Essentials: Oracle9i, Oracle8i and Oracle8, Second Edition

Chapter 4. Data Structures

In previous chapters, we examined some distinctions between the different components that make up an Oracle database. For example, you’ve learned that the Oracle instance differs from the files that make up the physical storage of the data in tablespaces, that you cannot access the data in a tablespace except through an Oracle instance, and that the instance itself isn’t very valuable without the data stored in those files.

In the same way, the actual tables and columns within the database are the entities stored within the database files and accessed through the database instance. The user who makes a request for data from an Oracle database probably doesn’t know anything about instances and tablespaces, but does know about the structure of her data, as implemented with tables and columns. To fully leverage the power of Oracle, you must understand how the Oracle Database Server implements and uses these logical data structures.

Datatypes

The datatype is one of the attributes for a column or a variable in a stored procedure. A datatype describes and limits the type of information stored in a column, as well as some of the operations that you can perform on columns with a particular datatype.

You can divide Oracle datatype support into three basic varieties: character datatypes, numeric datatypes, and datatypes that represent other kinds of data. You use all of these datatypes when you create columns in a table, as with this SQL statement:

CREATE SAMPLE_TABLE( ...