In the previous chapters, we examined some distinctions between the different components that make up an Oracle database. For example, we pointed out 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.
The instance is the logical entity used by applications and users, separate from the physical storage of data. In a similar way, the actual tables and columns are logical entities within the physical database. 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, the topic of this chapter.
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, and can limit the operations that you can perform on columns.
You can divide Oracle datatype support into three basic varieties: character datatypes, numeric datatypes, and datatypes that represent other kinds of data. You can use any of these datatypes when you create columns in a table, as with this SQL statement:
