Program with PL/SQL

Lesson 5

Working with Composite Data Types

Composite Data Types

• Are of two types– PL/SQL RECORDS– PL/SQL Collections

•INDEX BY Table• Nested Table•VARRAY

• Contain internal components

• Are reusable

PL/SQL Records

• Must contain one or more components of any scalar, RECORD, or INDEX BY table data type, called fields

• Are similar in structure to records in a third generation language (3GL)

• Are not the same as rows in a database 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:

Where field_declaration is:

TYPE type_name IS RECORD(field_declaration[, field_declaration] …);

Identifier type_name;

field_name {field_type | variable%TYPE| table.column%TYPE | table%ROWTYPE}[[NOT NULL] {:= | DEFAULT} expr]

PL/SQL Record Structure

100 King AD_PRES

Field1 (data type) Field2 (data type) Field3 (data type)

Field1 (data type) Field2 (data type) Field3 (data type)

Employee_id number(6) Last_name varchar2(25) Job_id varchar2(10)

Example:

The %ROWTYPE Attribute

• Declare a variable according to a collection of columns in a database table or view

• Prefix %ROWTYPE with the database table

• Fields in the record take their names and data types from the columns of the table or view

Advantages of Using %ROWTYPE

• The number and data types of the underlying database columns need not be known

• The number and data types of the underlying database column may change at run time

• The attribute is useful when retrieving a row with the SELECT * statement

INDEX BY Tables

• Are composed of two components:– Primary key of data type BINARY_INTEGER– Column of scalar or record data type

• Can increase in size dynamically because they are unconstrained

Creating an INDEX BY TableSyntax:

Declare an INDEX BY table to store names

Example:

TYPE type_name IS TABLE OF{column_type | variable%TYPE| table.column%TYPE} [NOT NULL]| table.%ROWTYPE[INDEX BY BINARY_INTEGER];

Identifier type_name;

. . .TYPE ename_table_type IS TABLE OF

employee.last_name%TYPEINDEX BY BINARY_INTEGER;

Ename_table ename_table_type;

INDEX BY Table Structure

. . .

1

2

3

. . .

. . .

Jones

Smith

Maduro

. . .

Unique identifier

BINARY_INTEGER

Column

Scalar

Using INDEX BY Table Methods

The following methods make INDEX BY tables easier to use:

– EXISTS– COUNT– FIRST and LAST– PRIOR– NEXT– TRIM– DELETE

Writing Executable Statement

PL/SQL Block Syntax and Guidelines

• Statements can be split across line, but keywords must not split

• Lexical units can be classified as:– Delimiters– Identifiers– Literals

• Character and date literals must be enclosed in single quotation marks

• Numbers can be simple values or scientific notation

– Comments

Identifiers

• Can contain up to 30 characters• Must begin with an alphabetical character• Can contain numerals, dollar signs,

underscores, and nuber signs• Cannot contain characters such as

hyphens, slashes, and spaces• Should not have the same name as a

database table column name• Should not be reserved words

Commenting Code

• Prefix single-line comments with two dashes (--)

• Place multiple-line comments between the symbols /* and */

SQL Functions in PL/SQL

• Available in procedural statements:– Single-row number– Single-row character– Data type conversion– Date– Timestamp – GREATEST and LEAST– Miscellaneous functions

• Not available in procedural statements– DECODE– Group functions

Nested Blocks and Variable Scope

• PL/SQL blocks can be nested wherever an executable statement is allowed

• A nested block becomes a statements• An exception section can contain nested

blocks• The scope of an identifier is that region of

a program unit (block, subprogram, or package) from which you can reference the identifier

Identifier Scope

An identifier is visible in the regions where you can reference the identifier without having to qualify it:

– A block can look up to the enclosing block– A block cannot look down to enclosed

blocks

Qualify an Identifier

• The qualifier can be the label of an enclosing block

• Qualify an identifier by using the block label prefix

Determining Variable Scope<<outer>>DECLARE

v_sal NUMBER(7,2) := 60000;v_comm NUMBER(7,2) := v_sal * 0.20;v_message VARCHAR2(255) := ‘eligible for

commision’;BEGIN

DECLAREv_sal NUMBER(7,2) := 50000;v_comm NUMBER(7,2) := 0;v_total_comp NUMBER(7,2) := v_sal + v_comm;

BEGINv_message := ‘CLERK not’||v_message;outer.v_comm := v_sal * 0.30;

END;v_message := ‘SALESMAN’||v_message;

END;

Operators in PL/SQL

• Logical

• Arithmetic

• Concatenation

• Parentheses to control order of operations

• Exponential operator (**)

Rules of Precedence

Operator Operation** Exponentiation

+, - Identity, negation

*, / Multiplication, division

+. -, || Addition, subtraction, concatenation

=, <. >, <=, >=, <>, !=, ~=, ^=, IS NULL, LIKE, BETWEEN, IN

Comparison

NOT Logical negation

AND Conjunction

OR Inclusion

Programming Guidelines

Make code maintenance easier by:

• Documenting code with comments

• Developing a case convention for tho code

• Developing naming conventions for identifies and other objects

• Enhancing readability by indenting