This Oracle/SQL tutorial provides a detailed introduction to the SQL query language and the Oracle Relational Database Management System ...

A table is uniquely identiï¬ ed by its name and consists of rows that contain the stored informa- tion, each row containing exactly one tuple (or record ). A table can have one or more columns. A column is made up of a column name and a data type, and it describes an attribute of the tuples. The structure of a table, also called relation schema, thus is deï¬ ned by its attributes. The type of information to be stored in a table is deï¬ ned by the data types of the attributes at table creation time.

SQL uses the terms table, row, and column for relation, tuple, and attribute, respectively. In this tutorial we will use the terms interchangeably.

A table can have up to 254 columns which may have diï¬ erent or same data types and sets of values (domains), respectively. Possible domains are alphanumeric data (strings), numbers and date formats.

The Oracle data dictionary is one of the most important components of the Oracle DBMS. It contains all information about the structures and objects of the database such as tables, columns, users, data ï¬ les etc. The data stored in the data dictionary are also often called metadata. Although it is usually the domain of database administrators (DBAs), the data dictionary is a valuable source of information for end users and developers. The data dictionary consists of two levels: the internal level contains all base tables that are used by the various DBMS software components and they are normally not accessible by end users. The external level provides numerous views on these base tables to access information about objects and structures at diï¬ erent levels of detail.

Source: dbis.ucdavis.edu