Advanced Databases
PL/SQL Anonymous Blocks
1
What is PL/SQL?
 Procedural programming language
 Uses detailed instructions
 Processes statements sequentially
 Combines SQL commands with
procedural instructions
 Used to perform sequential
processing using an Oracle
database
2
PL/SQL Variables

Variable names must follow the Oracle
naming standard



Can use reserved words (BEGIN, NUMBER) and
table names for variable names, but is not a good
practice
Make variable names descriptive
Use lower-case letters, and separate words
with underscores

Example: current_s_id
3
Declaring PL/SQL Variables

PL/SQL is a strongly-typed language


All variables must be declared prior to use
Syntax for declaring a variable:
variable_name data_type_declaration;

Example:
current_s_id NUMBER(6);
4
PL/SQL Data Types

Scalar


Composite


References a data structure
Reference (Not Required)


References a single value
References a specific database item
LOB (Not Required)

References a large binary object
5
Scalar Data Types

Database scalar data types:






VARCHAR2
CHAR
DATE
LONG
NUMBER
Non-database scalar data types:



Integers: BINARY_INTEGER, INTEGER, INT, SMALLINT
Decimal numbers: DEC, DECIMAL, DOUBLE,
PRECISION, NUMERIC, REAL
BOOLEAN
6
Composite Data Types


Reference multiple data elements, such
as a record
Types:



RECORD
TABLE
VARRAY

Tabular structure that can expand or contract
as needed
7
Reference Data Types (Not
Required)


Reference a database item
Assume data type of item


%TYPE: assumes data type of field
%ROWTYPE: assumes data type of entire
row
8
PL/SQL Program Structure
DECLARE
Variable declarations
Variable
Declarations
BEGIN
Program statements
Body
EXCEPTION
Error-handling statements
END;
Exception
Section
9
PL/SQL Program Lines
 May span multiple text editor lines
 Each line ends with a semicolon
 Text is not case sensitive
10
Comment Statements
 Block of comments are delimited with
/* */
/* <comment that spans more than one
line of code> */

Single comment line starts with 2
hyphens
-- comment on a single line
11
Arithmetic Operators
Example
Result
**
Exponentiation
2 ** 3
8
*
Multiplication
2*3
6
/
Division
9/2
4.5
+
Addition
3+2
5
-
Subtraction
3–2
1
-
Negation
-5
Negative 5
12
Assignment Statements
 Assignment operator: :=
 Variable being assigned to a new value
is on left side of assignment operator
 New value is on right side of operator
student_name := ‘John Miller’;
student_name := current_student;
13
Displaying PL/SQL Output
in SQL*Plus
 Normally PL/SQL is used with other Oracle
utilities such as forms or reports
 You will learn to use PL/SQL in SQL*Plus
 Command to activate memory buffer in
SQL*Plus to enable output from PL/SQL
programs:
SQL> SET SERVEROUTPUT ON SIZE buffer_size;
SQL> SET SERVEROUTPUT ON SIZE 4000;
14
Displaying PL/SQL Program
Output in SQL*Plus
 Command to output data from a PL/SQL
program in SQL*Plus:
DBMS_OUTPUT.PUT_LINE(‘output string’);
DBMS_OUTPUT.PUT_LINE(‘Current Output:’);
15
Executing a PL/SQL Program
in SQL*Plus
 Copy program code from Notepad to
SQL*Plus
 Type / to execute
16
PL/SQL Data Type Conversion
Functions
 TO_DATE: character string to DATE
TO_DATE(‘07/14/01’, ‘MM/DD/YY’);
 TO_NUMBER: character string to NUMBER
TO_NUMBER(‘2’);
 TO_CHAR: NUMBER or DATE to character string
TO_CHAR(2);
TO_CHAR(SYSDATE, ‘MM/DD/YYYY HH:MI’);
17
Character String Functions
 Concatenating strings: joining 2 or more
character strings into a single string
 Concatenation operator: ||
s_first_name := ‘Sarah’
s_last_name := ‘Miller’
s_full_name := s_first_name || ‘ ’
|| s_last_name
18
PL/SQL Character String
Functions
 RTRIM: removes blank trailing spaces
cust_address := RTRIM(cust_address);
 LENGTH: returns string length (number of
characters)
address_length := LENGTH(cust_address);
 UPPER, LOWER: changes characters to all upper
or lower case
s_name := UPPER(s_name);
s_name := LOWER(s_name);
19
PL/SQL Character String
Functions
 INSTR: searches a string and looks for a
matching substring and returns its starting
position
starting_position :=
INSTR(string_being_searched,
search_string>);
blank_position :=
INSTR(‘Sarah Miller’, ‘ ’);
20
PL/SQL Character String
Functions
 SUBSTR: extracts a specific number of
characters from a string, starting at a given
point
extracted_string :=
SUBSTR(string_being_searched,
starting_point,
number_of_characters_to_extract);
s_first_name := SUBSTR(‘Sarah Miller’, 1,5);
21
Debugging PL/SQL Programs
 Syntax error
 Does not follow language guidelines
 Causes a PLS- compile error
 Examples: misspelling a reserved word,
using a function incorrectly
 Logic error
 Program compiles correctly, but does not
give correct output
22
Locating and Correcting
Syntax Errors
 Isolate the line that is causing the error
 This may be before or after the line that is
flagged by the compiler
 Comment out lines as necessary until
program runs
 One error may cause several cascading
errors, so re-run program after fixing
each error
23
Locating and Fixing Logic
Errors
1. Identify the output variable(s) that have the
error.
2. Identify the inputs and calculations that
contribute to the error.
3. Display the values of the inputs using
DBMS_OUTPUT commands.
4. Take a break and look at it again later.
5. Ask a fellow student for help.
6. Ask your instructor for help.
24
NULL Values in Assignment
Statements



Until a value is assigned to a variable,
the variable’s value is NULL
Performing an arithmetic value on a
NULL value always results in a NULL
value
Advice: Always initialize variable values
25
PL/SQL
Selection
Structures
IF/THEN
 IF/END IF:
IF condition THEN
program statements
END IF;
 IF/ELSE/END IF:
IF condition THEN
program statements
ELSE
alternate program statements
END IF;
26
PL/SQL Selection Structures
 IF/ELSIF:
IF condition1 THEN
program statements;
ELSIF condition2 THEN
alternate program statements;
ELSIF condition3 THEN
alternate program statements;
. . .
ELSE
alternate program statements;
END IF;
27
PL/SQL Comparison Operators
Operator
Description
Example
=
Equal
Count = 5
<>, !=
Not Equal
Count <> 5
>
Greater Than
Count > 5
<
Less Than
Count < 5
>=
Greater Than or Equal
To
Count >= 5
<=
Less Than or Equal To
Count <= 5
28
Evaluating NULL Conditions in
IF/THEN Structures


If a condition evaluates as NULL, then it
is FALSE
How can a condition evaluate as NULL?


It uses a BOOLEAN variable that has not
been initialized
It uses any other variable that has not
been initialized
29
Using SQL Commands in
PL/SQL Programs
SQL Command Purpose
Category
Data Definition Change
Language (DDL) database
structure
Examples
CREATE,
ALTER,
GRANT,
REVOKE
Data
View or change SELECT,
Manipulation
data
INSERT,
Language (DML)
UPDATE,
DELETE
Transaction
Create logical COMMIT,
Control
transactions
ROLLBACK
Can be
used in
PL/SQL
No
Yes
Yes
30
PL/SQL Loops
 Loop: repeats one or more program
statements multiple times until an exit
condition is reached
 Pretest loop: exit condition is tested
before program statements are executed
 Posttest loop: exit condition is tested after
program statements are executed
31
LOOP … EXIT Loop
LOOP … EXIT
LOOP
program statements
IF condition THEN
Pretest
EXIT;
OR
Posttest
END IF;
more program statements
END LOOP;
32
LOOP … EXIT WHEN Loop
LOOP
program statements
EXIT WHEN condition;
END LOOP;
Posttest
33
WHILE Loop
WHILE condition
LOOP
program statements
END LOOP;
Pretest
WHILE … LOOP
34
Numeric FOR Loop
FOR counter_variable
IN start_value .. end_value
LOOP
Preset
program statements
number of
END LOOP;
iterations
35
Cursors


Pointer to a server memory location
Contains information about a SQL
command in a PL/SQL program

Called the command’s context area
36
Cursors
Database Server Memory
Cursor
context
area
active set
Number of
rows
processed
CID
1
2
3
4
5
CALLID
MIS 101
MIS 301
MIS 441
CS 155
MIS 451
Parsed
command
statement
CNAME
Intro. to Info. Systems
Systems Analysis
Database Management
Programming in C++
Client/Server Systems
CCREDIT
3
3
3
3
3
37
Types of Cursors
 Implicit
 Explicit
38
Implicit Cursors
 Created automatically every time you use an
INSERT, UPDATE, DELETE, or SELECT
command
 Doesn’t need to be declared
 Can be used to assign the output of a SELECT
command to one or more PL/SQL variables
 Can only be used if query returns one and
only one record
39
Implicit Cursor Syntax
SELECT field1, field2, …
INTO variable1, variable2, …
FROM tablename
WHERE
search_condition_that_will_
return_a_single_record;
40
Explicit Cursors
 Must be declared in program DECLARE
section
 Can be used to assign the output of a
SELECT command to one or more PL/SQL
variables
 Can be used if query returns multiple
records or no records
41
Using an Explicit Cursor
 Declare the cursor
 Open the cursor
 Fetch the cursor result into PL/SQL
program variables
 Close the cursor
42
Declaring an Explicit Cursor
DECLARE
CURSOR cursor_name IS
SELECT_statement;
43
Opening an Explicit Cursor
OPEN cursor_name;
44
Fetching Explicit Cursor
Records
FETCH cursor_name INTO
variable_name(s);
45
Closing an Explicit Cursor
CLOSE cursor_name;
46
Processing an Explicit Cursor

LOOP ..EXIT WHEN approach:
OPEN cursor_name;
LOOP
FETCH cursor_name INTO
variable_name(s);
EXIT WHEN cursor_name%NOTFOUND:
END LOOP;
CLOSE cursor_name;
47
Processing an Explicit Cursor

Cursor FOR Loop approach:
FOR variable_name(s) in cursor_name LOOP
additional processing statements;
END LOOP;
48
Explicit Cursor Attributes
Attribute
Return Value
%NOTFOUND
TRUE when no rows left
to fetch; FALSE when
rows left to fetch
TRUE when rows left to
fetch; FALSE when no
rows left to fetch
Number of rows a cursor
has fetched so far
TRUE if cursor is open
and FALSE is cursor is
closed
%FOUND
%ROWCOUNT
%ISOPEN
49
Using Reference Data Types in
Explicit Cursor Processing
 Declaring a ROWTYPE reference variable:
DECLARE
reference_variable_name cursor_name%ROWTYPE;
 Referencing a ROWTYPE reference variable:
reference_variable_name.database_field_name
50
PL/SQL Example1
DECLARE
Emp_name VARCHAR2(10);
Cursor
c1 IS SELECT Ename FROM Emp_tab
WHERE Deptno = 20;BEGIN
OPEN c1;
LOOP
FETCH c1 INTO Emp_name;
EXIT WHEN c1%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(Emp_name);
END LOOP;
END;
51
PL/SQL Example2
DECLARE
Emp_number INTEGER := 9999;
Emp_name
emp.empname%type;
BEGIN
SELECT Ename INTO Emp_name FROM Emp_tab
WHERE Empno = Emp_number; -- no such number
DBMS_OUTPUT.PUT_LINE('Employee name is ' ||
Emp_name);
EXCEPTION WHEN NO_DATA_FOUND THEN
DBMS_OUTPUT.PUT_LINE('No such employee: ' ||
Emp_number);
END;
52
PL/SQL Tables
 Composed into two components:
 Primary Key
 Column of Scalar or record type
 Increased dynamically
 Similar to Arrays in programming languages
 Known as Objects of type tables
 Syntax
TYPE typename is TABLE OF
[column_type | variable%type]
[INDEX BY BINARY_IINTEGER];
Indentifier type_name;
53
PL/SQL Tables Declaration

There are two steps in the declaration
of a PL/SQL table.


First, you must define the table structure
using the TYPE statement.
Second, once a table type is created, you
then declare the actual table.
54
PL/SQL Table Declaration
Example:
DECLARE
-- Table structure definition
TYPE EmpNameType IS TABLE OF
Emp.empname%TYPE
INDEX BY BINARY_INTEGER;
-- Create the actual table
EmpTab EmpNameType;
SupTab EmpNameType;
BEGIN
NULL; -- ...
END;

55
Referencing and Modifying
PL/SQL table rows





In order to specify a particular row in a PL/SQL table,
you must name the table and the index.
Syntax: <table_name>(<index_value>)
The datatype of the index value must be compatible
with the BINARY_INTEGER datatype.
You assign values to a row using the standard
assignment operator.
Referencing a nonexistent row raises the
NO_DATA_FOUND exception.
56
Referencing and Modifying
PL/SQL table rows
Example:
DECLARE
CURSOR c_Ename IS
SELECT empname, empno
FROM emp
ORDER BY empname;
TYPE type_Ename_tab IS TABLE OF emp.empname%TYPE
INDEX BY BINARY_INTEGER;
tab_Ename type_Ename_tab;
v_Ename_counter NUMBER := 0;
BEGIN
FOR r_Ename IN c_Ename
LOOP
v_Ename_counter := v_Ename_counter + 1;
tab_Ename(v_Ename_counter):= r_Ename.empname;
END LOOP;
END;
FOR i_Ename IN 1 .. v_Ename_counter
LOOP
DBMS_OUTPUT.PUT_LINE('Here is a name: '|| Tab_Ename(i_Ename));
END LOOP;
57
PL/SQL TABLE ATTRIBUTES

Here are seven PL/SQL table attributes you can use to gain information
about a PL/SQL table or to modify a row in a PL/SQL table:
• DELETE—Deletes rows in a table.
• EXISTS—Return TRUE if the specified entry exists in the table.
• COUNT—Returns the number of rows in the table.
• FIRST—Returns the index of the first row in the table.
• LAST—Returns the index of the last row in the table.
• NEXT—Returns the index of the next row in the table after the
specified row.
• PRIOR—Returns the index of the previous row in the table be-for
the specified row.
58
PL/SQL Table Attributes – How to
use them?
PL/SQL table attributes are used with the following syntax:
<table_name>.<attribute>

If you declare a PL/SQL table named t_emp then you get a rowcount
for the table as follows:
v_count := t_emp.count;

The DELETE, EXISTS, NEXT and PRIOR attributes function differently than the other
attributes.
These two generally operate on one row at a time, so you must
add the following syntax:
<TableName>.<attribute>(<IndexNumber>[,<IndexNumber>])
Examples:
t.emp.delete deletes all rows from the t_emp table, whereas
t_emp.delete(15) deletes the fifteenth row of the t_emp table.

Likewise, t_emp.exists(10) returns a value of true if there is a tenth row and a value of false
if there is not.
The EXISTS attribute can be used to determine if a particular index value
exists in the PL/SQL table or not.
NEXT and PRIOR is used in the same manner
59
PL/SQL Exception Handling


All error handling statements are placed
in the EXCEPTION program block
Exception handler: program command
that provides information about an
error, and suggest correction actions
60
Predefined Exceptions
 Common errors that have been given
predefined names that appear instead of
error numbers
Error Code
ORA-00001
ORA-01001
ORA-01403
ORA-01422
Exception Name
DUP_VAL_ON_INDEX
INVALID_CURSOR
NO_DATA_FOUND
TOO_MANY_ROWS
ORA-01476 ZERO_DIVIDE
ORA-01722 INVALID_NUMBER
ORA-06502 VALUE_ERROR
Description
Unique constraint violated
Illegal cursor operation
Query returns no records
Query returns more rows than
expected
Division by zero
Invalid numeric conversion
Error in arithmetic or numeric
function operation
61
Exception Handler Syntax
For Predefined Exceptions
WHEN exception1_name
exception handling
WHEN exception2_name
exception handling
…
WHEN OTHERS THEN
exception handling
THEN
statements;
THEN
statements;
statements;
62
Undefined Exceptions
 Less-common errors that have not been
given predefined names
 ORA- error code appears
 Exception handler tests for ORA- error
code and provides alternate error
message
63
User-Defined Exceptions
 Errors that will not cause a run-time
error, but will violate business rules
(i.e. they are created for logical errors)
 Programmer creates a custom error
message
64
Nested PL/SQL Program
Blocks

An inner
program
block can
be nested
within an
outer
program
block
DECLARE
variable declarations
BEGIN
program statements
DECLARE
variable declarations
BEGIN
program statements
EXCEPTION
error handling statements
END;
Outer
block
Inner
block
EXCEPTION
error handling statements
END;
65
Exception Handling in Nest
Program Blocks

If an exception is raised and handled in
an inner block, program execution
resumes in the outer block
66
Exception Handling in Nested
Program Blocks
DECLARE
variable declarations
BEGIN
program statements
DECLARE
exception_A
BEGIN
RAISE exception_A
EXCEPTION
exception_A error handler
END;
additional program statements
EXCEPTION
error handling statements
END;
Exception is raised and
handled in inner block
Program execution
resumes here
67
Exception Handling in Nested
Program Blocks

Exceptions raised in inner blocks can be
handled by exception handlers in outer
blocks
68
Example of a USER-DEFINED
Exception
Declare
huge_quantity
exception;
V_qty number(10);
v_msg varchar2(100);
Begin
v_qty := &V_qty;
if v_qty > 1000 then
v_msg := ‘very huge quantity’;
raise huge_quantity;
else
v_msg := ‘Good’;
end if;
dbms_output.put_line (v_msg);
Exception
when huge_quantity then
dbms_output.put_line (v_msg);
End;
69
Example of a USER-DEFINED Exception
(Giving an error number between -20000 to
-20999)
Declare
huge_quantity
exception;
V_qty number(10);
v_msg varchar2(100);
Begin
v_qty := &V_qty;
if v_qty > 1000 then
v_msg := ‘very huge quantity’;
raise huge_quantity;
else
v_msg := ‘Good’;
end if;
dbms_output.put_line (v_msg);
Exception
when huge_quantity then
raise_application_error (-20100, v_msg);
End;
70