15. Teradata SQL

Structured Query Language (SQL)

Structured Query Language (SQL) is the language used to access the

database. It is sometimes referred to as a Fourth Generation Language

(4GL) to differentiate it from Third Generation Languages such as

FORTRAN and COBOL, though it is quite different from other 4GLs. It

acts as an intermediary between the user and the database. SQL defines

the answer set that is returned from the database.

SQL is different from other computer languages. Its statements resemble

English-like structures. It provides powerful, set-oriented database

manipulation including

structural modification, data retrieval,

modification

, and security functions.

There are four important subsets of SQL: the Data Definition Language,

the Data Manipulation Language, Data Control Language and Stored

Procedure Language.

Data Definition Language (DDL)

DDL allows a user to define the

database objects and the relationships

that exist among them

. Examples of DDL uses are creating or modifying

tables and views.

Data Manipulation Language (DML)

DML consists of the

statements that manipulate, change, or retrieve

the data rows

of the database. If the DDL defines the database, the DML

lets the user change the information contained in the database. The DML

is the most commonly used subset of SQL. It is used to select, update,

delete, and insert rows.

Data Control Language (DCL)

DCL is used to

restrict or permit a user's access. It can selectively limit

a user's ability to retrieve, add, or modify data. It is used to grant and

revoke access privileges on tables and views.

Stored Procedure Language (SPL)

SPL is used to

create and call stored procedures in Teradata.

Teradata Extensions to SQL

User Assistance commands allow you to list the objects in a database or

the characteristics of a table, see how a query will execute, or show the

details of your system. They vary widely from vendor to vendor.