Procedural SQL – Part of Chapter 7
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Procedural SQL
 Shortcomings of SQL
SQL doesn’t support execution of a stored set of procedures
based on some logical condition.
 SQL fails to support the looping operations.
 No handling of sequence of operations

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 Solutions

Embedded SQL



Shared Code



To remedy the above shortcomings, SQL statements can be inserted
within the procedural programming language
The embedded SQL approach involves the duplication of application
code in many programs.
Critical code is isolated and shared by all application programs.
This approach allows better maintenance and logic control.
Procedural SQL (Oracle’s version of persistent stored modules)
Procedural SQL
 Procedural SQL
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
Procedural SQL allows the use of procedural code
and SQL statements that are stored within the
database.

The procedural code is executed by the DBMS
when it is invoked by the end user.

End users can use procedural SQL (PL/SQL) to
create:




Anonymous PL/SQL blocks
Triggers
Stored procedures
PL/SQL functions
Anonymous PL/SQL Block Examples
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SHOW ERRORS
 Can help diagnose errors found in PL/SQL blocks
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 Yields additional debugging information whenever an
error is generated after an PL/SQL block is created or
executed
Anonymous PL/SQL Block
with Variables and Loops
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Procedural SQL
 Triggers

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A trigger is procedural SQL code that is
automatically invoked by the RDBMS upon the
occurrence of a data manipulation event.

A trigger is always invoked before or after a data
row is selected, inserted, or updated.

A trigger is always associated with a database table.

Each database table may have one or more triggers.

A trigger is executed as part of the transaction that
triggered it.
Procedural SQL

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Role of triggers

Triggers can be used to enforce constraints that
cannot be enforced at the design and
implementation levels.

Triggers add functionality by automating critical
actions and providing appropriate warnings and
suggestions for remedial action.

Triggers can be used to update table values, insert
records in tables, and call other stored procedures.

Triggers add processing power to the RDBMS and
to the database system.
Triggers
 Oracle recommends triggers for:

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Auditing purposes (creating audit logs)
 Automatic generation of derived column values
 Enforcement of business or security constraints
 Creating replica tables for backup purposes
The Revised PRODUCT Table
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Procedural SQL
 Syntax to create a trigger in ORACLE
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CREATE OR REPLACE TRIGGER <trigger_name>
[BEFORE/AFTER][DELETE/INSERT/UPDATE OF
<column_name] ON <table_name>
[FOR EACH ROW]
BEGIN
PL/SQL instructions;
……………
END;
Creating Trigger
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 To ensure academic year doesn’t get out of synch
with credits earned
CREATE OR REPLACE TRIGGER trg_cred_updated
AFTER UPDATE OF credits ON students
BEGIN
UPDATE students
SET Year = ‘Sr’
WHERE credits >= 90;
… also do juniors, sophs
END;
Creation of the Oracle Trigger for the PRODUCT Table
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The P_REORDER Value Mismatch
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The Second Version of the PRODUCT_REORDER Trigger
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Figure 7.34
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Variation on Figure 7.35
The P_REORDER Flag Has Not Been Properly Set After
Increasing the P_ONHAND Value
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Variation on Figure 7.36
The Third Version of the Product Reorder Trigger
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Figure 7.37
Execution of the Third Trigger Version
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Figure 7.38
Procedural SQL
 Stored Procedures
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
A stored procedure is a named collection of procedural
and SQL statements.

Stored procedures are stored in the database and
invoked by name.

Stored procedures are executed as a unit.

The use of stored procedures reduces network traffic,
thus improving performance.
Stored Procedures: Advantages
 Substantially reduce network traffic and increase
performance
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 No transmission of individual SQL statements over
network
 Help reduce code duplication by means of code
isolation and code sharing
 Minimize chance of errors and cost of application
development and maintenance
Procedural SQL
 Syntax to create a stored procedure
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CREATE OR REPLACE PROCEDURE procedure_name
(argument IN/OUT data-type, etc)
IS/AS BEGIN
DECLARE variable name and data type
PL/SQL or SQL statements;
END;
 Syntax to invoke a stored procedure
EXEC store_procedure_name (parameter,
parameter, …)
Creating and Invoking A Simple Stored Procedure
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No Longer a Figure
The PROD_SALE Stored Procedure
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No Longer a Figure
Executing the PROD_SALE Stored Procedure
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No Longer a Figure
Creating the PRC_PROD_DISCOUNT
Stored Procedure
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Results of the PRC_PROD_DISCOUNT
Stored Procedure
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Stored Procedure with Parameter
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CREATE OR REPLACE PROCEDURE prc_prod_discount2
(wpi IN NUMBER) AS
BEGIN
IF ((wpi <= 0) OR (wpi >= 1)) THEN – validate param
DBMS_OUTPUT.PUT_LINE(‘Error – bad pct’);
ELSE
UPDATE product
SET p_discount = p_discount + wpi
WHERE p_onhand >= p_min * 2;
DBMS_OUTPUT.PUT_LINE(‘Update Successful’);
END IF;
END;
/
Calling Stored Procedure With Parameter
SQL> EXEC prc_prod_discount2 (1.5); -- will get error
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SQL> EXEC prc_prod_discount2 (.05); -- will work like
original
The PRC_CUS_ADD Stored
Procedure
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The PRC_INV_ADD and
PRC_LINE_ADD Stored Procedures
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Testing the PRC_INV_ADD and
PRC_LINE_ADD Procedures
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Cursor Processing Commands
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Cursor Attributes
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Stored Procedures
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 Advantage – can be used to encapsulate an entire
business transaction – group statements together as
a transaction and don’t let them be separated
 Advantage – code resides at the DB and is executed
at the DB – less communication – faster processing
 Advantage – reduce redundant code – since code
that Would be repeated is in a procedure that can be
written once and called multiple times.
 Used 1) when transaction involves updating multiple
tables OR 2) for complex business rules or
constraints
Procedural SQL
 PL/SQL Stored Functions
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
A stored function is a named group of procedural
and SQL statements that returns a value.

Syntax to create a function:
CREATE FUNCTION function_name (argument IN
data-type, etc)
RETURN data-type
AS BEGIN
PL/SQL statements;
RETURN (value); ……
END;

Stored procedures can be called from triggers or
stored procedures
Embedded SQL
 SQL code embedded within host language (COBOL, C++, ASP,
Java, Visual Basic, …) program
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 Embedded SQL Framework:

A standard syntax to identify SQL statements (EXEC SQL/ END-EXEC)

A standard syntax to identify host variables (:varname for host program
variables within SQL statements)

A communication area used to exchange status and error information
between SQL and the host language (SQLCODE and SQLSTATE variables)
 Alternative interface – programs use a Call Level Interface (CLI) in
which the programmer uses an Application Programming Interface
(API) such as ODBC (Windows) or JDBC (Java)
Static SQL
 Embedded SQL in which the programmer used predefined
SQL statements and parameters
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
End users of programs are limited to actions that were specified in
application programs
 SQL statements will not change while application is running
Using (Static) Embedded SQL
 Programmer writes embedded SQL inside host language
 Preprocessor transforms embedded SQL into specialized
procedure calls that are DBMS and language-specific
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
Preprocessor provided by the DBMS vendor
 The program is compiled using host language compiler

Compiler creates object code module with DBMS procedure calls
 Object code is linked to respective library modules and
generates executable

Binds DBMS procedure calls to DBMS run-time libraries.
 Binding process typically creates an “access plan” module that
contains instructions to run the embedded code at run time
 Executable is run and embedded SQL statements retrieve
data from the DB
Using (Static) Embedded SQL
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EXEC SQL
SQL statement
END-EXEC
 To be useful, statement probably can’t do the same thing
every time the program is run – need variables
 Variables declared in host language
 Inside SQL statement, precede with :
 E.g.
EXEC SQL
DELETE FROM students WHERE stdID = :toDel;
END-EXEC;
 E.g.
EXEC SQL
SELECT max(GPA) INTO :maxGpa
FROM students;
END_EXEC;
Using Static Embedded SQL
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 As with PL/SQL, embedded SQL requires the use of cursors to
hold multi-results queries
 Declare cursor
EXEC SQL
DECLARE StdCursor FOR
SELECT stdID, LName, FName
FROM Students
WHERE major = ‘Dart’;
END-EXEC
 Open cursor
EXEC SQL
OPEN StdCursor;
END-EXEC
 Fetch next record
EXEC SQL
FETCH StdCursor INTO :stdID, :last, :first;
END-EXEC
IF SQLCODE = 0 THEN
… do whatever is necessary
Dynamic SQL
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 SQL statement is not known in advance, but instead is
generated at run time
 Program can generate SQL statements at run time that are
required to respond to ad hoc queries
 Attribute list and the condition are not known until the end
user specifies them
 Tends to be much slower than static SQL
 Requires more computer resources
 More likely to be incompatibilities among DBMS vendors
Dynamic SQL Example
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SELECT :W_ATTRIBUTE_LIST
FROM :W_TABLE
WHERE :W_CONDITION
 Variables are text variables which are built as the
program executes
End Procedural SQL
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