03 Writing Control Structures, Writing with Compatible Data Types Using Explicit Cursors

3-1 Copyright © 2006, Oracle. All rights reserved.
Writing Control Structures
Working with Composite
Data Types
Using Explicit Cursors

3
Copyright © 2006, Oracle. All rights reserved.
Working with Composite
Data Types

Composite Data Types
• Can hold multiple values (unlike scalar types)
• Are of two types:
– PL/SQL records
– PL/SQL collections
– INDEX BY tables or associative arrays
– Nested table
– VARRAY

Composite Data Types
• Use PL/SQL records when you want to store
values of different data types but only one
occurrence at a time.
• Use PL/SQL collections when you want to store
values of the same data type.

PL/SQL Records
• Must contain one or more components (called
fields) of any scalar, RECORD, or INDEX BY table
data type
• Are similar to structures in most 3GL languages
(including C and C++)
• Are user defined and can be a subset of a row in a
table
• Treat a collection of fields as a logical unit
• Are convenient for fetching a row of data from a
table for processing

Creating a PL/SQL Record
Syntax:
TYPE type_name IS RECORD
(field_declaration[, field_declaration]…);
field_name {field_type | variable%TYPE
| table.column%TYPE | table%ROWTYPE}
[[NOT NULL] {:= | DEFAULT} expr]
identifier type_name;
1
2
field_declaration:

PL/SQL Record Structure
Example
100 King AD_PRES
employee_id number(6) last_name varchar2(25) job_id varchar2(10)
Field2 (data type) Field3 (data type)Field1 (data type)
Field2 (data type) Field3 (data type)Field1 (data type)

%ROWTYPE Attribute
• Declare a variable according to a collection of
columns in a database table or view.
• Prefix %ROWTYPE with the database table or view.
• Fields in the record take their names and data
types from the columns of the table or view.
Syntax:
DECLARE
identifier reference%ROWTYPE;

Advantages of Using %ROWTYPE
• The number and data types of the underlying
database columns need not be known—and in fact
might change at run time.
• The %ROWTYPE attribute is useful when retrieving a
row with the SELECT * statement.

INDEX BY Tables or Associative Arrays
• Are PL/SQL structures with two columns:
– Primary key of integer or string data type
– Column of scalar or record data type
• Are unconstrained in size. However, the size
depends on the values that the key data type can
hold.

Creating an INDEX BY Table
Syntax:
Declare an INDEX BY table to store the last names of
employees:
TYPE type_name IS TABLE OF
{column_type | variable%TYPE
| table.column%TYPE} [NOT NULL]
| table%ROWTYPE
[INDEX BY PLS_INTEGER | BINARY_INTEGER
| VARCHAR2(<size>)];
identifier type_name;
...
TYPE ename_table_type IS TABLE OF
employees.last_name%TYPE
INDEX BY PLS_INTEGER;
...
ename_table ename_table_type;

INDEX BY Table Structure
Unique key Value
... ...
1 Jones
5 Smith
3 Maduro
... ...
PLS_INTEGER Scalar

Using INDEX BY Table Methods
The following methods make INDEX BY tables easier
to use:
• EXISTS
• COUNT
• FIRST and LAST
• PRIOR
• NEXT
• DELETE

INDEX BY Table of Records
Define an INDEX BY table variable to hold an entire row
from a table.
Example
DECLARE
TYPE dept_table_type IS TABLE OF
departments%ROWTYPE
INDEX BY PLS_INTEGER;
dept_table dept_table_type;
-- Each element of dept_table is a record

Nested Tables
1
2
3
4
..
2 GB
Bombay
Sydney
Oxford
London
....

Bombay
Sydney
Oxford
London
....
VARRAY
Tokyo
1
2
3
4
..
10

3
Copyright © 2006, Oracle. All rights reserved.
Using Explicit Cursors

Cursors
Every SQL statement executed by the Oracle server
has an associated individual cursor:
• Implicit cursors: Declared and managed by
PL/SQL for all DML and PL/SQL SELECT
statements
• Explicit cursors: Declared and managed by the
programmer

Explicit Cursor Operations
Active set
Table
100 King AD_PRES
101 Kochhar AD_VP
102 De Haan AD_VP
. . .
. . .
. . .
139 Seo ST_CLERK
140 Patel ST_CLERK
. . .

Controlling Explicit Cursors
• Load the
current
row into
variables.
FETCH
• Test for
existing
rows.
EMPTY?
• Return to
FETCH if
rows are
found.
No
• Release the
active set.
CLOSE
Yes
• Create a
named
SQL area.
DECLARE
• Identify the
active set.
OPEN

Controlling Explicit Cursors
Fetch a row.
Close the cursor.
Cursor
pointer
Open the cursor.1
2
3
Cursor
pointer
Cursor
pointer

Cursor FOR Loops
Syntax:
• The cursor FOR loop is a shortcut to process
explicit cursors.
• Implicit open, fetch, exit, and close occur.
• The record is implicitly declared.
FOR record_name IN cursor_name LOOP
statement1;
statement2;
. . .
END LOOP;

Explicit Cursor Attributes
Obtain status information about a cursor.
Boolean Evaluates to TRUE if the cursor is
open
Evaluates to TRUE if the most recent
fetch does not return a row
Evaluates to TRUE if the most recent
fetch returns a row; complement of
%NOTFOUND
Evaluates to the total number of
rows returned so far
Boolean
Boolean
Number
%ISOPEN
%NOTFOUN
D
%FOUND
%ROWCOUN
T
Attribute Type Description

Cursors with Parameters
Syntax:
• Pass parameter values to a cursor when the
cursor is opened and the query is executed.
• Open an explicit cursor several times with a
different active set each time.
CURSOR cursor_name
[(parameter_name datatype, ...)]
IS
select_statement;
OPEN cursor_name(parameter_value,.....) ;

FOR UPDATE Clause
Syntax:
• Use explicit locking to deny access to other
sessions for the duration of a transaction.
• Lock the rows before the update or delete.
SELECT ...
FROM ...
FOR UPDATE [OF column_reference][NOWAIT | WAIT n];

WHERE CURRENT OF Clause
Syntax:
• Use cursors to update or delete the current row.
• Include the FOR UPDATE clause in the cursor query
to lock the rows first.
• Use the WHERE CURRENT OF clause to reference the
current row from an explicit cursor.
WHERE CURRENT OF cursor ;
UPDATE employees
SET salary = ...
WHERE CURRENT OF emp_cursor;

Class 3: Overview
This practice covers the following topics:
• Performing iterative steps by using the loop
structure
• Declaring INDEX BY tables
• Processing data by using INDEX BY tables
• Declaring a PL/SQL record
• Processing data by using a PL/SQL record

Class 3: Overview
This practice covers the following topics:
• Declaring and using explicit cursors to query rows
of a table
• Using a cursor FOR loop
• Applying cursor attributes to test the cursor status
• Declaring and using cursors with parameters
• Using the FOR UPDATE and WHERE CURRENT OF
clauses

03 Writing Control Structures, Writing with Compatible Data Types Using Explicit Cursors

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