13. Teradata objects

Teradata Objects

A

database in the Teradata system is a collection of objects known as

tables

, views, macros, triggers and stored procedures. Databases

provide a

logical grouping for information. They are also the

foundation for space allocation and access control.

1) Tables

A table is the logical structure of data in an RDBMS. It is a

twodimensional

structure made up of columns and rows

. A user defines

a table by giving it a table name that refers to the type of data that will be

stored in the table (e.g., an Employee table stores data about employees.)

A

column represents attributes of the table. Column names are given to

each column of the table. All information in a column is of the same type.

For example, a column named Date of Birth would only hold date of birth

information. Each occurrence of an entity is stored in the table as a

row.

Entities are the people, places, things, or events that the table is

describing. Tables require Permanent Space to store rows.

2) Views

A view is a

pre-defined subset of one or more tables or other views. It

does not exist as a real table, but serves as a reference to existing tables

or views. One way to think of a view is as a virtual table. Views have

definitions in the Data Dictionary (DD) but do not contain any physical

rows. Views can be used to control access to the underlying tables.

Views can be used to hide columns from users, to insulate applications

from database changes, and to standardize or simplify access techniques.

Views do not require Permanent Space.

3) Macros

A macro is a predefined, stored set of one or more SQL commands and

report-formatting commands. Macros are used to simplify the execution of

frequently used SQL commands. Macros do not require Permanent

Space.

4) Triggers

A trigger is an event-driven procedure attached to a table. A trigger

defines events that happen when some other event, called a

triggering

event

, occurs. A trigger consists of one or more SQL statements that are

associated with a table and are executed when the trigger is fired. A

trigger is created with the CREATE TRIGGER statement.

5) Stored Procedures

A stored procedure is a pre-defined set of statements invoked through a

single SQL CALL statement. Stored procedures may contain both

Teradata SQL statements and procedural statements (in Teradata,

referred to as Stored Procedure Language, or SPL). Macros are similar to

stored procedures but do not contain SPL.