Chapter List

Overview

Let's start the examination of tuning SQL with descriptions of the various basic SQL commands used in relational databases, leading on to the Oracle database specifically.

SQL is pronounced "Es-Queue-Ell" or "Sequel", depending on the source and location of your training. The meaning of the acronym SQL is Structured Query Language. SQL is the language used to access data from a relational database such as Oracle Database. SQL was originally devised as a computer language with the development of the IBM relational database called System R. The idea of SQL originates from the relational data model. SQL is used to access subsets of data in the form of rows or tuples from a larger dataset. A dataset is represented by a related group of entities in a data model of a set of tables in an Oracle Database schema.

5.1 DML and DDL

Unlike other relational databases Oracle Database classifies and separates SQL commands into two distinct groups as shown in Figure 5.1. These two groups are DML or Data Manipulation Language commands, and DDL or Data Definition Language commands. There are two differences between DML and DDL commands:

Figure 5.1: DML Versus DDL

DML commands manipulate data. A DML command is a command that...