[bbk4998]第11集 Chapter 06 Working with Composite Data Types 004998(Record)

Objectives

After completing this lesson,you should be able to do the following:

• Describe PL/SQL collections and records
• Create user-defined PL/SQL records
• Create a PL/SQL record with the %ROWTYPE attribute
• Create associative arrays

Oracle数据库中，复合数据类型包含:集合(collections)、记录(records)

Oracle数据库中，集合的类型:(关联数组、嵌套表、可变长度数组)

Agenda

• Introducing composite data types
• Using PL/SQL records
  • -Manipulating data with PL/SQL records
  • -Advantages of the %ROWTYPE attribute
• Using PL/SQL collections
  • -Examining associative arrays(重点介绍)
  • -Introducing nested tables
  • -Introducing VARRAY

Composite Data Types

• Can hold multiple values (unlike scalar types)
• Are of two types:
  • -PL/SQL records
  • -PL/SQL collections
    • -Associate array(INDEX BY TABLE;以前称之为索引表)
    • -Nested table
    • -VARRAY

PL/SQL Records or Collections?

• 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.

Record相当于C语言里面的Struct

Collection类似于C语言里的Array

对于Record里面的每个组成部分，称为field，对于Collection里面的每个组成部分称之为element。

PL/SQL Records

• Must contain one or more components(called fields) of any sclar,RECORD,or INDEX BY table data type
• Are similar to structures in most third-generation 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
        (filed_declaration[,filed_declaration]...);

identify type_name;

filed_declaration:

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

Creating a PL/SQL Record:Example

SET SERVEROUT ON;
DECLARE
        TYPE t_rec IS RECORD
                (
                        v_sal number(8),
                        v_minsal number(8) default 1000,
                        v_hire_date employees.hire_date%type,
                        v_rec1 employees%rowtype
                );

        v_myrec t_rec;
BEGIN
        v_myrec.v_sal := v_myrec.v_minsal + 500;
        v_myrec.v_hire_date := sysdate;

        SELECT * INTO v_myrec.v_rec1 FROM employees WHERE employee_id = 100;

        DBMS_OUTPUT.PUT_LINE(v_myrec.v_rec1.last_name || '-->' || TO_CHAR(v_myrec.v_hire_date,'YYYY-MM-DD HH24:MI:SS') || '->'  || TO_CHAR(v_myrec.v_sal));
END;
/

声明一个类型，是不占内存的；而根据这个类型创建一个变量，是占内存的.

PL/SQL Record Structure

Field declarations:

Example:

 

%ROWTYPE Statement

• 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;

SET SERVEROUT ON;
DECLARE
        TYPE myrec IS RECORD
                (
                        id number(8),
                        name varchar2(20) default 'ArcerZhang',
                        birthday DATE
                );
        person myrec;
BEGIN
        person.id := 123456;
        person.birthday := SYSDATE;

        DBMS_OUTPUT.PUT_LINE(person.id || '-->' || person.name || '->' || TO_CHAR(person.birthday,'YYYY-MM-DD HH24:MI:SS'));
END;
/

Advantage of Using the %ROWTYPE Attribute

• 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 you want to retrieve a row with：
  • -The SELECT * statement
  • -Row-level INSERT and UPDATE statements

当使用%ROWTYPE进行record的定义时（假设基于table的定义），一旦table的结构发生变化，那么record所在的过程或者函数将失效，此时必须要重新编译.