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Pl/sql program and its various aspects

Pl is the short form of procedural language extension of sql which was developed in the 1990,s by the oracle corporation; pl/sql combines the procedural features of programming languages with sql. The programming languages combination improves and enhances the capabilities of sql. A pl/sql engine is used for processing pl/sql statements. The code of Pl/ sql is stored on the database or client system.

Introduction to pl/sql

The pl/sql supports loops, conditions, variables, exceptions and arrays. The array support is a bit unusual and uses the pl/sql collections. The version 8 of oracle database for pl/sql includes advanced features like object orientation. The code containing units of pl/sql program can be compiled on the oracle database. Thus the programmers can install and embed the pl/sql units into any database directly, which contain all the units of functionality.

Details of pl/sql

The oracle sql plus tools helps in script writing which contain pl/sql program units. These units can be read using the tool, directly into the database. Databases are stored with the program units, and can be executed at later times. Programmers can easily embed the data manipulation language statements into the database directly. But the data definition language requires the dynamic sql, which is a bit more complex, to write statements in the Pl/ sql program and code. Pl/sql codes of typical software applications require dml statements that constitute a majority of Pl / sql code. The recent versions of pl/sql use a native dynamic sol, which is simpler. The package functionality is increased by oracle foundation in successive oracle databases.

The sql statement is able to return multiple values and procedures cannot be used in the sql statement. Procedures are the specific and smaller pieces of code and are also termed as the workhorses of the world of coding. Procedures cannot be called from the sql but functions can be called. Sql distinguishes between the functions and procedures. The conceptually linked procedures, variables, functions, table statements, constants and cursors form the packages. Re use of codes is promoted by reuse of packages. The specification and the body comprise the two parts of packages. Although the body is excluded sometimes as it is not necessary. The specification is essential and forms the interface to various applications, and is also vital in declaring the variables, constants, types and subprograms which are available. A pl/sql program comprises of both sql and pl/sql statements which combine to from a pl/sql block.

The pl/sql block has basically three sections. This are-

1. The declaration section-the starting of this section of the pl/ sql block is done by the reserved keyword declare. The place holders are used for manipulation. This section is optional. Data in the execution section, for example, constants, variables, records, cursors are declared. Placeholders store data temporarily which can be variable, constant and records. The section also comprises of cursor declaration.

2. The execution section-the block starts with the reserved keyword begin and ends with the reserve keyword end. For performing any logic, the tasks are written in this section. This is a mandatory section. The execution section comprises of statements, conditional statements and loops.

3. The exception section-the section initiates with the reserved keyword of exception. This section is again optional. This section is crucial to the ending and termination of pl/sql block, since it checks all the errors of the program. The improper handling of the exceptions leads the block to terminate abruptly and with errors imbibed.

A semicolon must be used for ending all the sections and comments are used for code documentation.

Pl sql is similar to Sybase, db2, transact sql etc. The syntax of sql is modeled on the basis of ADA. Pascal is the common ancestor to both ADA and pl/sql. Hence you can find pl/sql resembling ADA in various aspects.