The most common type of table in an Oracle database is a relational table, which is structured with simple columns similar to the employees table. Two other table types are supported: object tables and XMLType tables. Any of the three table types can be defined as permanent or temporary. Temporary tables hold session-private data that exists only for the duration of a transaction or session. They are useful in applications where a results set must be held temporarily in memory, perhaps because the results set is constructed by running multiple operations.
You can build relational tables in either heap or index-organized structures. In heap structures, the rows are not stored in any particular order. In index-organized tables, the row order is determined by the values in one or more selected columns. For some applications, index-organized tables provide enhanced performance and more efficient use of disk space.
This section describes permanent, heap-organized tables. For information about other table types and when to use them, see Oracle Database Administrator's Guide and Oracle Database Concepts. For the syntax required to create tables with SQL, see Oracle Database SQL Language Reference.