Relational Database Management System

Database Procedural Programming
PL/SQL and Embedded SQL
By,
B.Nivegeetha
I-Msc cs.
Nadar Saraswathi College of Arts and Science,
Theni.

PL/SQL
 PL/SQL is Oracle's procedural language exte
nsion to SQL.
 PL/SQL combines SQL with the procedural fu
nctionality of a structured programming langu
age, such as IF ... THEN, WHILE, and LOOP.
 The PL/SQL engine used to define, compile,
and execute PL/SQL program units.
 A component of many Oracle products, includ
ing Oracle Server.

Procedures and Functions
 A set of SQL and PL/SQL statements grouped together as a
unit (block) to solve a specific problem or perform a set of re
lated tasks.
 An anonymous block is a PL/SQL block that appears within
your application and it is not named or stored in the databas
e. In many applications, PL/SQL blocks can appear whereve
r SQL statements can appear.
 A stored procedure is a PL/SQL block that Oracle stores in t
he database and can be called by name from an application.
 Functions always return a single value to the caller; procedu
res do not return values to the caller.
 Packages are groups of procedures and functions.

Procedure PL/SQL Example
CREATE PROCEDURE credit_labmark (sno NUMBER, cno CHAR, cre
dit NUMBER) AS
old_mark NUMBER;
new_mark NUMBER;
BEGIN
SELECT labmark INTO old_mark FROM enrol
WHERE studno = sno and courseno = cno FOR UPDATE OF la
bmark;
new_ mark := old_ mark + credit;
UPDATE enrol SET labmark = new_mark
WHERE studno = sno and courseno = cno;
COMMIT;
EXCEPTION
WHEN NO_DATA_FOUND THEN
INSERT INTO enrol(studno, courseno, labmark, exammark)
VALUES(sno, cno, credit, null);
WHEN OTHERS THEN ROLLBACK;
END credit_labmark;
PL/SQL sta
tement.
SQL statement.
Locks enrol
EXECUTE credit_lab
mark
(99234,’CS2312’,20)

Function
create function get_lab_mark(sno number, cno char)
return number
as f_lab_mark number;
no_mark exception;
begin
select labmark
into f_lab_mark from enrol
where studno = sno and courseno = cno;
if f_lab_mark is null
then raise no_mark;
else return(f_lab_mark);
end if
exception
when no_mark then …..return(null);
end;

Stored Procedures
Created in a user's schema and s
tored, centrally, in compiled for
m in the database as a named
object that can be:
 interactively executed by a user
using a tool like SQL*Plus
 called explicitly in the code of a d
atabase application, such as an
Oracle Forms or a Pre compiler a
pplication, or in the code of anoth
er procedure or trigger
When PL/SQL is not stored in the
database, applications can sen
d blocks of PL/SQL to the data
base rather than individual SQ
L statements  reducing netw
ork traffic. .
Program code
.
.
Program code
.
HIRE_EMP(…);
.
Program code
Program code
.
.
Program code
.
HIRE_EMP(…);
.
Program code
Program code
.
.
Program code
.
HIRE_EMP(…);
.
Program code HIRE_EMP(…)
BEGIN
.
.
END;
Database Applications
Stored
Procedure
Database

Architecture
Procedure
Begin
Procedurecall
Procedurecall
SQL
Procedurecall
SQL
End;
Procedural
Statement
Executor
PL/SQL Engine
SQL Statement
Executor
SQL
Database
Program code
Program code
Procedure call
Program code
Program code
SGA
Oracle Server
Database
Application

Benefits of Stored Procedures I
 Security
 Control data access through procedures and functions.
 E.g. grant users access to a procedure that updates a ta
ble, but not grant them access to the table itself.
 Performance
The information is sent only once between database and
application and thereafter invoked when it is used.
 Network traffic is reduced compared with issuing individu
al SQL statements or sending the text of an entire PL/S
QL block
 A procedure's compiled form is readily available in the d
atabase, so no compilation is required at execution time.
 The procedure might be cached

Benefits of Procedures II
 Memory Allocation
 Stored procedures take advantage of the shared memory capabiliti
es of Oracle
 Only a single copy of the procedure needs to be loaded into memor
y for execution by multiple users.
 Productivity
 By designing applications around a common set of procedures, you
can avoid redundant coding and increase your productivity.
 Procedures can be written to insert, update, or delete rows from a t
able and then called by any application without rewriting the SQL st
atements necessary to accomplish these tasks.
 If the methods of data management change, only the procedures n
eed to be modified, not all of the applications that use the procedur
es.

Benefits of Procedures III
 Integrity
 Stored procedures improve the integrity and consistenc
y of your applications. By developing all of your applicati
ons around a common group of procedures, you can re
duce the likelihood of committing coding errors.
 You can test a procedure or function to guarantee that it
returns an accurate result and, once it is verified, reuse i
t in any number of applications without testing it again.
 If the data structures referenced by the procedure are al
tered in any way, only the procedure needs to be recom
piled; applications that call the procedure do not necess
arily require any modifications.

Packages
 A method of encapsulating and storing related proced
ures, functions, variables, cursors and other package
constructs together as a unit in the database for conti
nued use as a unit.
 Similar to standalone procedures and functions, pack
aged procedures and functions can be called explicitl
y by applications or users.
 Organize routines
 Increased functionality (e.g. global package variab
les can be declared and used by any procedure in
the package) and
 Increased performance (e.g. all objects of the pac
kage are parsed, compiled, and loaded into memo
ry once).

Package manage tasks in database
 Database applications expli
citly call packaged procedu
res as necessary.
 After being granted the priv
ileges for the package, a us
er can explicitly execute an
y of the procedures contain
ed in it.
 EXECUTE marks_mgmt. cr
edit_labmark(99234,’CS23
12’,20)
 Packages offer several dev
elopment and performance
advantages over standalon
e stored procedures;
Program code
.
EMP_MGMT.FIRE_EMP(…);
Program code
.
EMP_MGMT.HIRE_EMP(…);
.
Program code
Program code
.
EMP_MGMT.HIRE_EMP(…);
Program code
.
EMP_MGMT.SAL_RAISE(…);
.
Program code
FIRE_EMP(…)
BEGIN
.
.
END;
HIRE_EMP(…)
BEGIN
.
.
END;
SAL_RAISE(…)
BEGIN
.
.
END;
Database

Benefits of Packages
 Encapsulation of related procedures and variables providing:
 Better organization during the development process and for granti
ng privileges
 Declaration of public and private procedures, variables, constants, an
d cursors
 Better performance
 An entire package is loaded into memory when a procedure withi
n the package is called for the first time in one operation, as oppo
sed to the separate loads required for standalone procedures. W
hen calls to related packaged procedures occur, no disk I/O is ne
cessary to execute the compiled code already in memory.
 A package body can be replaced and recompiled without affectin
g the specification. Objects that reference a package's constructs
(always via the specification) need not be recompiled unless the
package specification is also replaced. Unnecessary recompilatio
ns can be minimized, so in less impact on overall database perfor
mance.

Triggers vs Procedures and Packages
 Triggers are similar to stored procedures. A trigger ca
n include SQL and PL/SQL statements to execute as
a unit and can invoke stored procedures. Triggers are
stored in the database separate from their associated
tables.
 Procedures and triggers differ in the way that they ar
e invoked.
 A procedure is explicitly executed by a user, applic
ation, or trigger.
 Triggers (one or more) are implicitly fired (execute
d) by Oracle when a triggering INSERT, UPDATE,
or DELETE statement is issued, no matter which u
ser is connected or which application is being use
d.

Retrieval: Impedance Mismatch
 What happens when the query returns several rows? T
he host variables can only hold one value.
 Oracle will only pass the first row returned by the query
to the PL/SQL block (or host language program).
 Re-executing the SELECT operation will only run the q
uery again and so the first row will be selected again.
 Different type systems
 Different execution models

Cursors
 When a query returns multiple rows a cursor
must be declared to process each row return
ed by the query and to keep track of which ro
w is currently being processed.
 The rows returned by a query are stored in an
area called the Active Set.
 A cursor can be thought of as pointing to a ro
w in the active set.

Cursors and RetrievalPROCEDURE apply_marks IS
CURSOR marks_cursor IS
SELECT sno, cno, kind, amount FROM marks
WHERE status = 'Pending' ORDER BY time_tag FOR UPDATE OF
marks;
BEGIN
FOR marks IN marks_cursor LOOP /* implicit open and f
etch */
new_status := ’Accepted';
IF marks.kind = ’L' THEN
credit_labmark(marks.sno, marks.cno, marks.amount);
ELSIF trans.kind = ’E' THEN
credit_exammark(marks.sno, marks.cno, marks.amoun
t);
ELSE new_status := 'Rejected';
END IF;
UPDATE marks SET status = new_status
WHERE CURRENT OF marks_cursor;
END LOOP; COMMIT;
END apply_marks;

Embedded SQL
 SQL statements placed within a program. The source
program is called the host program, and the language
in which it is written is called the host language
 You can execute any SQL statement using embedde
d SQL statements just as if you were in SQL*Plus.
 CREATE, ALTER and DROP database tables
 SELECT, INSERT, UPDATE and DELETE rows of
data
 COMMIT transactions (make any changes to the d
atabase permanent)

Embedded SQL Statements
 Embedded SQL statements incorporate DDL, DML, and tran
saction control statements within a procedural language pro
gram. They are used with the Oracle pre-compilers, e.g. Pro
*C.
 Embedded SQL statements enable you to
 define, allocate, and release cursors (DECLARE CURSO
R, OPEN, CLOSE)
 declare a database name and connect to Oracle (DECLA
RE DATABASE, CONNECT)
 assign variable names (DECLARE STATEMENT)
 initialize descriptors (DESCRIBE)
 specify how error and warning conditions are handled (W
HENEVER)
 parse and execute SQL statements (PREPARE, EXECU
TE, EXECUTE IMMEDIATE)
 retrieve data from the database (FETCH).

Executable and Declarative Statements
 Embedded SQL includes all the interactive SQL statements pl
us others that allow you to transfer data between Oracle and
a host program. There are two types of embedded SQL state
ments:
 Executable:
 used to connect to Oracle, to define, query and manipulate
Oracle data, to control access to Oracle data and to proces
s transactions. They can be placed wherever host-languag
e executable statements can be placed.
 Declarative:
 do not operate on SQL data. Use them to declare Oracle o
bjects, communication areas and SQL variables which will
be used by Oracle and your host program. They can be pla
ced wherever host-language declarations can be placed.

Binding Variables
 A host variable is prefixed with a colon (:) in SQL statements bu
t must not be prefixed with a colon in C statements.
EXEC SQL BEGIN DECLARE SECTION;
INT sno;
VARCHAR cno[5];
INT labmark;
EXEC SQL END DECLARE SECTION;
…
EXEC SQL SELECT labmark INTO :labmark F
ROM enrol
WHERE studno = :sno and courseno = :cno
 The case of the host variable is significant when referencing the
m.
database attribute
host variable

SELECT
EXEC SQL SELECT courseno, subject
INTO :courseno, :subject
FROM course
WHERE courseno = :menu_selection;
Attributes in the staff table.
INTO clause specifies the host variables
which will hold the values of the attribute
s returned.
Host variable used to supply the WHERE claus
e with a value to base the query on.
In SQL*Plus this would be done using a literal
value. Pro*C allows variables to be used to sp
ecify a value. Host variables used in this way
must contain a value before the SELECT state
ment is used.

Example
Declare any host variables
EXEC SQL BEGIN DECLARE SECTION;
VARCHAR studname[21];
VARCHAR cno[5];
INT labmark;
VARCHAR o_connect_uid[18];
EXEC SQL END DECLARE SECTION;
Include the error handlers
EXEC SQL INCLUDE sqlca;
EXEC SQL INCLUDE oraca;
Log on procedure
void Oracle_Connect(void) {
(void)strcpy(o_connect_uid.arr,"/@t:ora-srv:mucs7");
o_connect_uid.len = strlen(o_connect_uid.arr);
EXEC SQL CONNECT :o_connect_uid;
}

Connect to Oracle Server and Do the Query
main()
{ EXEC SQL WHENEVER SQLERROR DO sqlerror()
EXEC ORACLE OPTION (ORACA=YES);
oraca.orastxtf = 1; Oracle_Connect(); printf("Connected to O
raclen");
 Cursor for query
EXEC SQL DECLARE studcursor CURSOR FOR
SELECT s.name, e.courseno, e.labmark,
FROM student s, enrol e WHERE s.studno = e.studno;
 Do the query
EXEC SQL OPEN studcursor; printf(”Name/Course/LabMark
n");
 Loop to fetch rows
while (sqlca.sqlcode == 0) {
EXEC SQL FETCH studcursor
INTO :studname, :cno, :labmark
printf("%s,%s,%d", studname, cno, labmark);
}
printf("%ld rows selected.n",sqlca.sqlerrd[2]);
EXEC SQL CLOSE studcursor;
EXEC SQL COMMIT WORK RELEASE;
exit(1);}

Examples of Packages and Procedures

Create Package Specification
create package marks_mgmt (null) as
max_mark CONSTANT NUMBER := 100.00;
PROCEDURE apply_marks;
PROCEDURE enter_marks(sno number,cno char
, kind char, credit number);
end marks_mgmt;

Create Package Body
CREATE PACKAGE BODY marks_mgmt AS
new_status CHAR(20); /* Global variable to record status of tra
nsaction being applied. Used for update in enter_marks. */
PROCEDURE do_journal_entry (sno NUMBER, cno CHAR, kind CH
AR) IS
/* Records a journal entry for each marks credit applied by the enter_
marks procedure. */
BEGIN
INSERT INTO journal
VALUES (sno, cno, kind, sysdate);
IF kind = ’L' THEN new_status := ’Lab credit';
ELSIF kind = ’E' THEN new_status := ’Exam credit';
ELSE new_status := 'New enrolment';
END IF;
END do_journal_entry;

Create Package Body I
CREATE PROCEDURE credit_labmark (sno NUMBER, cno CHAR,
credit NUMBER) AS
old_mark NUMBER; new_mark NUMBER;
mark_overflow EXCEPTION;
BEGIN
SELECT labmark INTO old_mark FROM enrol
WHERE studno = sno and courseno = cno
FOR UPDATE OF labmark;
new_ mark := old_ mark + credit;
IF new_mark <= max_mark THEN
UPDATE enrol SET labmark = new_mark
WHERE studno = sno and courseno = cno ;
do_journal_entry(sno, cno, L);
ELSE RAISE mark_overflow
ENDIF;

Create Package Body II
EXCEPTION
WHEN NO_DATA_FOUND THEN
/* Create new enrolment if not found */
INSERT INTO enrol (studno, courseno, labmark, exammark)
VALUES(sno, cno, credit, null);
do_journal_entry(sno, cno, 'N');
WHEN mark_overflow THEN
new_status := ’Mark Overflow’;
WHEN OTHERS THEN
/* Return other errors to application */
new_status := 'Error: ' || SQLERRM(SQLCODE);
END credit_labmark;
CREATE PROCEDURE credit_exammark (sno NUMBER, cno CHAR, cr
edit NUMBER) AS…
END credit_exammark;

PROCEDURE apply_marks IS …. complete shortly...
END apply_marks;
PROCEDURE enter_marks(sno NUMBER, cno CHAR, kind CHAR
, credit NUMBER) IS
/* A new mark is always put into this 'queue' before b
eing applied to the specified enrolment instance by
the APPLY_MARKS procedure. */
BEGIN
INSERT INTO marks
VALUES (sno, cno, kind, amount, 'Pending', sysdate);
COMMIT;
END enter_marks;
END marks_mgmt ; /* end package */
Create Package Body

An error handling procedure
void sqlerror(void)
{ int o_errl;
int len = 550;
char o_err[550];
EXEC SQL WHENEVER SQLERROR CONTINUE;
sqlca.sqlerrm.sqlerrmc[sqlca.sqlerrm.sqlerrml] = NULL;
printf("nOracle Error:n%s", sqlca.sqlerrm.sqlerrmc);
oraca.orastxt.orastxtc[oraca.orastxt.orastxtl] = NULL;
printf("ERROR statement:%sn", oraca.orastxt.orastxtc);
sqlglm(o_err, &len, &oerrl);
o_err[o_errl] = NULL;
printf("ERROR Details: %sn",o_err);
oraca.orasfnm.orasfnmc[oraca.orasfnm.orasfnml] = NULL;
printf("ERROR at line %ld in %sn", oraca.oraslnr,oraca
.orasfnm.orasfnmc);
EXEC SQL ROLLBACK WORK RELEASE;

Relational Database Management System

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