表集合的extend属性

Extend 扩展元素的个数，且在使用下标时，只能到1到这个整个个数的范围：

CREATE or replace type list_of_name is table of varchar2(1000);

declare

happyfamily list_of_name:=list_of_name();--必须在使用的时候初始化，此处初始化为一个空元素,此处若不初始化，必须在体部初始化

children list_of_name:=list_of_name();

parents list_of_name:=list_of_name();

l_row BINARY_INTEGER;

begin

happyfamily.extend(5);--extend(4)是在最后一个元素后面增加4个元素

happyfamily(2):='a';

happyfamily(3):='b';

happyfamily(4):='c';

happyfamily(5):='d';

l_row:=happyfamily.first;

WHILE(l_row IS NOT NULL) LOOP

dbms_output.put_line('the name is :'||happyfamily(l_row));

l_row:=happyfamily.next(l_row);

END LOOP;

end;

结果：

the name is :

the name is :a

the name is :b

the name is :c

the name is :d

很显然，下标1没有，如果我们改一下：

CREATE or replace type list_of_name is table of varchar2(1000);

declare

happyfamily list_of_name:=list_of_name();--必须在使用的时候初始化，此处初始化为一个空元素,此处若不初始化，必须在体部初始化

children list_of_name:=list_of_name();

parents list_of_name:=list_of_name();

l_row BINARY_INTEGER;

begin

happyfamily.extend(5);--extend(4)是在最后一个元素后面增加4个元素

happyfamily(2):='a';

happyfamily(3):='b';

happyfamily(4):='c';

happyfamily(6):='d';

l_row:=happyfamily.first;

WHILE(l_row IS NOT NULL) LOOP

dbms_output.put_line('the name is :'||happyfamily(l_row));

l_row:=happyfamily.next(l_row);

END LOOP;

end;

结果：

   

很显然：extend所使用的下标值不能超过extend指定的值。