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When defining a table, the designer must first decide what kind of data will be stored in each column.
The datatype of the column affects low-level implementation details such as how much storage space is allocated to each data item and the operations that can be performed on the data. The datatypes used in a relational database correspond closely to those used in other programming languages; however they are not defined by any agreed standard, and so there are slight variations between different database platforms (Oracle, SQL Server, etc.). The datatypes most commonly used in Oracle are shown in the table below.

Datatype Used for Example
NUMBER(n) Integer values with up to n digits -10, 0, 1024
NUMBER(n, m) Floting point values of up to n digits including m decimal places 3.14159, -10.5
VARCHAR2(n) Variable character string of maximum length n 'Edinburgh'
DATE A combined date and time value 10-JAN-2011 12:24:00

Like other database platforms, Oracle provides a range of other datatypes that are suitable for more specific requirements, or which improve the storage efficiency. You can find details in the Oracle documentation.

Further reading

Built-in Data Types

SQL Data Types