Download ADVANCED SQL AND PL/SQL TOPICS

Advanced SQL And
PL/SQL Topics
Chapter 9
A Guide to Oracle9i
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Lesson A Objectives
• Learn how to create and use indexes
• Become familiar with PL/SQL stored program units
• Learn how to create server-side stored program units
in SQL*Plus
• Learn how to use Forms Builder to create stored
program units
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Database Indexes
• Similar to an index in a book
• Table with list of sorted data values and
corresponding physical location
• Used to speed searches
• Uses ROWID column to represent physical location
• Primary key indexed automatically
• Unlimited number allowed, but more indexes means
more processing time for action queries (insert,
update, delete)
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Creating an Index
• Create index after table data is loaded
• CREATE INDEX index_name ON tablename
(index_fieldname);
• Convention for naming index: tablename_fieldname.
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Composite Index
• Contains multiple (up to 16) sorted columns
• Used for queries with multiple search conditions
• CREATE INDEX index_name ON
tablename(index_fieldname1, index_fieldname2, …);
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Viewing Index Information
• Use data dictionary view USER_INDEXES
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Dropping an Index
• If an index is no longer needed or does not
improve performance, delete it
• DROP INDEX index_name;
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Use an Index When
• Table contains a large number of records (a rule of
thumb is that a large table contains over 100,000
records)
• The field contains a wide range of values
• The field contains a large number of NULL values
• Application queries frequently use the field in a
search condition or join condition
• Most queries retrieve less than 2% to 4% of the table
rows
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Do Not Use an Index When
• The table does not contain a large number of records
• Applications do not use the proposed index field in a
query search condition
• Most queries retrieve more than 2% to 4% of the
table records
• Applications frequently insert or modify table data
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Overview of PL/SQL
Stored Program Units
• Self-contained group of program statements
that can be used within a larger program.
• Easier to conceptualize, design, and debug
• Save valuable programming time because
you can reuse them in multiple database
applications
• Other PL/SQL programs can reference them
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Overview of PL/SQL
Stored Program Units
• Server-side program units — stored in the
database as database objects and execute
on the database server
• Client-side program units — stored in the file
system of the client workstation and execute
on the client workstation
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Types of Program Units
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Creating Stored Program Units
• Procedure: a program unit that can receive multiple input
parameters and return multiple output values or return no output
values
• Function: a program unit that can receive multiple input
parameters, and always returns a single output value.
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Parameter Declarations List
• Defines the parameters and declares their
associated data types
• Enclosed in parentheses
• Separated by commas
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Parameter Declarations List
• Parameter mode describes how the program unit can
change the parameter value:
– IN - specifies a parameter that is passed to the program unit
as a read-only value that the program unit cannot change.
– OUT - specifies a parameter that is a write-only value that
can appear only on the left side of an assignment statement
in the program unit
– IN OUT - specifies a parameter that is passed to the
program unit, and whose value can also be changed within
the program unit
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Creating a Stored Procedure
in SQL*Plus
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Debugging Stored Program
Units in SQL*Plus
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Debugging Stored Program
Units in SQL*Plus
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Calling a Stored Procedure
• From SQL*Plus command line:
– EXECUTE procedure_name (parameter1_value,
parameter2_value, ...);
• From PL/SQL program:
– Omit execute command
• Passing parameters (see Figure 9-13)
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Creating a Stored Program Unit
Function
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Creating a Stored
Program Unit Function
• Last command in function must be RETURN
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Calling a Function
• variable_name := function_name(parameter1,
parameter2, ...);
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Using Forms Builder to Create
Stored Procedures and Functions
• Create and test the program unit within a form
• Save it as a stored program unit in your database
schema
• Provides an enhanced development and debugging
environment:
– Color-coded editor for entering and debugging program unit
commands
– Displays compile error messages immediately
– Use the Forms Debugger to step through program unit
commands and view how variable values change
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Using Forms Builder to Create
Stored Procedures and Functions
• Create the procedure or function as a form
program unit
• Test and debug the form program unit by
calling it from commands within a form trigger
• Save the form program unit as a stored
program unit in the database
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Lesson B Objectives
• Learn how to call stored procedures from other
stored procedures and pass parameter values
• Create libraries
• Create packages
• Create database triggers
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Calling Stored Program Units
from Other Stored Program Units
• Decompose applications into logical units of work and
then write individual program units for each logical
unit
• Code is in a single location
• Developers do not need to rewrite program units that
already exist
• References procedures must be declared first
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PL/SQL Libraries
• Operating system file that contains code for multiple
related procedures and functions
• Attach a PL/SQL library to a form or report
– Triggers within the form or report reference library’s
procedures and functions
• Store a PL/SQL library in the file system of the client
workstation
• .pll extension - stands for “PL/SQL Library”
• Compile the library into a library executable file - .plx
extension - stands for “PL/SQL Library Executable”
• Library places the commands for multiple related
program units in a single location that developers can
access and use
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Creating a PL/SQL Library
• Use Forms Builder to create libraries
• Add form program units and stored program units to
the library.
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Packages
• Another way to make PL/SQL program units available
to multiple applications
• A code library that contains related program units and
variables
• Stored in the database and executes on the database
server
• Have more functionality than PL/SQL libraries:
–
–
–
–
Can create variables in packages
Definitions for explicit cursors
More convenient to use than PL/SQL libraries
Available without explicitly attaching them to a form or report
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Package Specification
• Also called package header
• Declares package objects, including
variables, cursors, procedures, and functions,
• Use to declare public variables:
– Remain in memory after the programs that declare
and reference them terminate
– Declared in the DECLARE section of a package
– Referenced same as private variables
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Package Specification
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Package Header
• Package_name identifies the package
– Must adhere to the Oracle Naming Standard
• Declare the package objects in any order
• Package can consist of just variable
declarations, or it can consist of just
procedure or function declarations
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Procedure and Function Declarations
• Declare a procedure:
PROCEDURE procedure_name
(parameter1 parameter1_data_type,
parameter2 parameter2_data_type, ...);
• Declare a function:
FUNCTION function_name
(parameter1 parameter1_data_type,
parameter2 parameter2_data_type, ...)
RETURN return_datatype;
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Package Body
• Contains the implementation of declared
procedures and functions
• Specification comes before body
• Optional: sometimes a package contains
only variable or cursor declarations, and no
procedure or function declarations
• See Figure 9-35 for general syntax
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Package Body
• Package_name in the package body must be the
same as package_name in the package specification
• Variables that you declare at the beginning of the
package body are private to the package
• Each package program unit has its own declaration
section and BEGIN and END statements
• Each program unit declared in the package body
must have a matching program unit forward
declaration in the package specification, with an
identical parameter list
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Creating a Package Header in
SQL*Plus
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Creating a Package Body in
SQL*Plus
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Using Package Objects
• Must preface the item with the package
name:
– package_name.item_name.
• To grant other users the privilege to execute a
package:
– GRANT EXECUTE ON package_name TO
username;
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Creating a Package in Forms Builder
•
•
•
•
•
•
Create a program unit of type Package Spec
Type the package specification in the PL/SQL editor
Create a program unit of type Package Body
Type package body in the PL/SQL editor
Compile package body and test using a form trigger
Save the package in the database for future use
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Database Triggers
• Program units that execute in response to the
database events of inserting, updating, or deleting a
record
• Different from form triggers
• Useful for maintaining integrity constraints and audit
information
• Cannot accept input parameters
• Executes only when its triggering event occurs
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Trigger Properties
• Trigger timing:
– Defines whether a trigger fires before or after the
SQL statement executes
– Can have the values BEFORE or AFTER
• Trigger statement:
– Defines the type of SQL statement that causes a
trigger to fire
– Can be INSERT, UPDATE, or DELETE
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Trigger Properties
• Trigger level:
– Defines whether a trigger fires once for each triggering
statement or once for each row affected by the triggering
statement
– Can have the values ROW or STATEMENT
– Statement-level triggers fire once, either before or after the
SQL triggering statement executes.
– Row-level triggers fire once for each row affected by the
triggering statement
• Use :OLD.fieldname to reference previous value
• Use :NEW.fieldname to reference changed value
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Creating Database Triggers
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Database Trigger Header
• Trigger_name must follow Oracle Naming Standard
• Join statement types using the OR operator to fire for
multiple statement types (INSERT OR UPDATE)
• WHEN (condition) clause:
– Trigger will fire only for rows that satisfy a specific search
condition
– WHEN OLD.grade IS NOT NULL;
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Database Trigger Body
• Contains the commands that execute when the
trigger fires
• PL/SQL code block that contains the usual
declaration, body, and exception sections
• Cannot contain transaction control statements
• Reference the NEW and OLD field values only in a
row-level trigger
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Trigger Use – Audit Trail
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Creating Audit Trigger in SQL*Plus
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Creating a Database Trigger
in Forms Builder
• Use the Database Trigger Dialog Box to
specify trigger properties
• Type trigger body into Trigger Body entry field
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Disabling and Dropping Triggers
• To remove a trigger:
– DROP TRIGGER trigger_name;
• To disable/enable a trigger:
– ALTER TRIGGER trigger_name [ENABLE |
DISABLE];
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Viewing Trigger Information
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Summary
• Database indexes store an ordered list of field values
with corresponding ROWID
• Indexes are used to speed query performance
• Stored program units are named PL/SQL blocks that
are saved
• Procedures accept parameters and return 0,1, or
many values
• Functions accept parameters and return exactly one
value
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Summary
• PL/SQL Library is a client-side file containing
procedures and functions
• PL/SQL Package is a collection of public variables,
cursors, procedures and functions stored in the
DBMS
• Database triggers are PL/SQL blocks that are run in
response to table changes
• Database triggers are used to enforce integrity
constraints and track changes
• Forms Builder may be used as an IDE to develop
functions, procedures, libraries, packages and
triggers
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