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Definition: Structured
Query Language (SQL) is the set of statements with which all programs and
users access data in an Oracle database.
RDBMS: Dr. E. F.
Codd published the paper, "A Relational Model of Data for Large Shared
Data Banks", in June 1970. Codd’s model is now accepted as the definitive
model for relational database management systems (RDBMS). Today, SQL is
accepted as the standard RDBMS language.
What is SQL & its
features:
SQL is a data sub language. The purpose of SQL is to
provide an interface to a relational database such as Oracle, and all SQL
statements are instructions to the database.
Among the
features of SQL are the following:
It processes sets of data as
groups rather than as individual units.
It provides automatic
navigation to the data.
It uses statements that are complex and
powerful individually, and that therefore stand alone. Flow-control
statements were not part of SQL originally, but they are found in the
recently accepted optional part of SQL, ISO/IEC
Standards &
Compliance:
The latest SQL standard published by ANSI and ISO is
often called SQL92 (and sometimes SQL2). The formal names of the new
standard are:
ANSI X3.135-1992, "Database Language SQL"
ISO/IEC
9075:1992, "Database Language SQL"
SQL92 defines four levels of
compliance: Entry, Transitional, Intermediate, and Full.
A
conforming SQL implementation must support at least Entry SQL. Oracle8i
fully supports Entry SQL and has many features that conform to
Transitional, Intermediate, or Full SQL.
Use of
SQL
Essentially, SQL lets you work with data at the logical level.
You need to be concerned with the implementation details only when you
want to manipulate the data.
SQL provides statements for a
variety of tasks, including:
Querying data
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.
Porting & Support
All major relational
database management systems support SQL, so you can transfer all skills
you have gained with SQL from one database to another. In addition, all
programs written in SQL are portable. They can often be moved from one
database to another with very little modification.
Embedded
SQL:
Embedded SQL refers to the use of standard SQL statements
embedded within a procedural programming language.
Lexical
Conventions:
1. An Oracle SQL statement can include one or more
tabs, carriage
returns, spaces, or comments anywhere a space occurs
within the definition of the
statement.
2. Case is
insignificant in reserved words, keywords, identifiers and
parameters.
However, case is significant in text literals and quoted
names.
Basic Elements of SQL:
The basic elements of
Oracle SQL are simplest building blocks of SQL statements.
Literals (Text, Integer, Number), Datatypes, Format Models,
Nulls, Pseudocolumns, Comments, Database Objects, Schema Object Names and
Qualifiers, Referring to Schema Objects and Parts
Literals
The terms literal and
constant value are synonymous and refer to a fixed data value. Character
literals are enclosed in single quotation marks.
You can specify
character literals with the ’text’ notation, national character literals
with the N’text’ notation, and numeric literals with the integer or number
notation, depending on the context of the
literal.
Datatypes
Each literal or column value
manipulated by Oracle has a datatype. A value’s datatype associates a
fixed set of properties with the value. These properties cause Oracle to
treat values of one datatype differently from values of another.
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