Oracle7 Server SQL Reference
How SQL Works
This section describes many of the reasons for SQL's widespread acceptance by relational database vendors as well as end users. The strengths of SQL benefit all ranges of users including application programmers, database administrators, management, and end users.
Technically speaking, SQL is a data sublanguage. That is to say, the purpose of SQL is to interface to a relational database such as Oracle7, and all SQL statements are instructions to the database. In this it differs from general purposes programming languages like C and Basic. Among the features of SQL are the following:
- it processes sets of data as groups rather than as individual units
- it uses statements that are complex and powerful individually, and that therefore stand alone. The flow-control statements of most programming languages are absent in SQL, although they are provided in Oracle's extension to standard SQL called PL/SQL.
Essentially, SQL lets you work with data at the logical level, only being concerned with the implementation details when you want to manipulate them. For example, to retrieve a set of rows from a table, you define a condition used to filter the rows. All rows satisfying the condition are retrieved in a single step and can be passed as a unit to the user , to another SQL statement, or to an application. You need not deal with the rows one by one, nor do you have to worry about how they are physically stored or retrieved. All SQL statements use the optimizer, a part of Oracle7 that determines the fastest means of accessing the specified data. Oracle7 also provides techniques you can use to make the optimizer perform its job better.
SQL provides commands for a variety of tasks including:
- inserting, updating, and deleting rows in a table
- creating, replacing, altering, and dropping objects
- controlling access to the database and its objects
- guaranteeing database consistency and integrity
SQL unifies all of the above tasks in one consistent language.
Common Language for All Relational Databases
Because all major relational database management systems support SQL, you can transfer all skills you have gained with SQL from one database to another. In addition, since all programs written in SQL are portable, they can often be moved from one database to another with very little modification.