Fundamental Structured Query Language (SQL) Teradata

The access language for all modern relational database systems (RDBMS) is Structured Query Language (SQL). It has evolved over time to be the standard. The ANSI SQL group defines which commands and functionality all vendors should provide within their RDBMS.

There are three levels of compliance within the standard: Entry, Intermediate and Full. The three level definitions are based on specific commands, data types and functionalities. So, it is not that a vendor has incorporated some percentage of the commands; it is more that each command is categorized as belonging to one of the three levels. For instance, most data types are Entry level compliant. Yet, there are some that fall into the Intermediate and Full definitions.

Since the standard continues to grow with more options being added, it is difficult to stay fully ANSI compliant. Additionally, all RDBMS vendors provide extra functionality and options that are not part of the standard. These extra functions are called extensions because they extend or offer a benefit beyond those in the standard definition.

At the writing of this book, Teradata was fully ANSI Entry level compliant based on the 1992 Standards document. NCR also provides much of the Intermediate and some of the Full capabilities. This book indicates feature by feature which SQL capabilities are ANSI and which are Teradata specific, or extensions. It is to NCR's benefit to be as compliant as possible in order to make it easier for customers of other RDBMS vendors to port their data warehouse to Teradata.

As indicated earlier, SQL is used to access, store, remove and modify data stored within a relational database, like Teradata. The SQL is actually comprised of three types of statements. They are: Data Definition Language (DDL), Data Control Language (DCL) and Data Manipulation Language (DML). The primary focus of this book is on DML and DDL. Both DDL and DCL are, for the most part, used for administering an RDBMS. Since the SELECT statement is used the vast majority of the time, we are concentrating on its functionality, variations and capabilities.

Everything in the first part of this chapter describes ANSI standard capabilities of the SELECT command. As the statements become more involved, each capability will be designated as either ANSI or a Teradata Extension.

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