Relation, Attributes and Tuple

By | July 2, 2015

In relational database system data are represented using tables (Also known as relations.). A query issued against the DBS (Database system) also results in a table.  A table is uniquely identified by its name and consists of rows and columns. A table has the following structure:

Figure-2 Table Structure

A table is consists of rows that contain the stored information, 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 and attribute of the tuple. The structure of table, also called relation schema, thus id defined by its attributes.

SQL uses the terms table, row and column for relation, tuple and attributes respectively. A table can have up to 254 columns which may have different or same sets (or data types) of values (domains). Possible domains are alphanumeric data (Strings), Numbers and Date formats.  The type of information to be stored in a table is defined by the data types of the attributes at table creation time.

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