集合
集合有3中類型:
- 變長數組:類似於java中的數組。可存儲有序的元素集合,每個元素都有一個索引,記錄了元素在數組中的位置。只能作爲整體來修改。在創建時創建時可設置最大大小,但是後期可以更改。
- 嵌套表:嵌套在另一個表中的表。可以插入、更新和刪除嵌套標表中的單個元素。沒有最大大小,可以再嵌套表中存儲任意數目的元素。
- 關聯數組(以前稱爲索引表);類似於java中的散列表。是個鍵值對集合。關聯數組只能用於PL/SQL中,不能存儲在數據庫中。
一.創建集合類型
1.創建變長數組類型
既可以是內置的數據庫類型,也可以是用戶定義的對象類型。
crete type t_varray_address as varray(3) of varchar2(50);
修改最大大小,將最大元素個數改爲10
alter type t_varray_address modify limit 10 cascade;
2.創建嵌套表類型
create type t_address as object (
street varchar2(15),
city varchar2(15),
state char(2),
zip varchar2(5)
);
create type t_nested_table_address as table of t_address;
二.使用集合類型定義表列
1.使用變長數組類型定義表列
create table customer_with_varry (
id integer primary key,
first_name varchar(10),
last_name varchar(10),
addresses t_varray_address
);
注意:當變長數組的大小小於4000字節時,變長數組的元素直接存儲在表中;否則,變長數組存儲在表之外。當變長數組存儲在表中時,它的元素訪問速度比嵌套表的元素訪問速度快。
2.使用嵌套表類型定義表列
create table customer_with_nested_tabel (
id integer primary key,
first_name varchar(10),
last_name varchar(10),
addresses t_nested_table_address
)
nested table
addresses
store as
nested_addresses;
三.獲取集合信息
1.獲取變長數組信息
describe t_varray_address
t_varray_address varray(3) of varchar2(50);
select * from user_varrays where type_name='t_varray_address';
2.獲得嵌套表信息
describe t_nested_table_address
select *
from user_nested_tables
where table_name='nested_addresses';
四.填充集合元素
1.填充變長數組元素
insert into customer_with_varry values (
1, 'Steve', 'Brown',
t_varray_address (
'2 State Street, Beantown, MA, 12345'
)
);
2.填充嵌套表元素
insert into customer_with_nested_tabel values(
1, 'Steve', 'Brown',
t_nested_table_address (
t_address('2 State Street, Beantown, MA, 12345')
)
);
五.檢索集合元素
1.檢索變長數組元素
select *
from customer_with_varry
where id = 1;
ID FIRST_NMAE LAST_NAME ASSRESSES
-----------------------------------------------------------
1 Steve Brown t_varray_address('2 State Street, Beantown, MA, 12345')
2.檢索嵌套表元素
select *
from customer_with_nested_tabel
where id = 1;
ID FIRST_NMAE LAST_NAME ASSRESSES
-----------------------------------------------------------------
1 Steve Brown t_nested_table_address(t_address('2 State Street, Beantown, MA, 12345'))
六.使用table()函數將集合視爲一系列行
1.將table()函數應用於變長數組
select a.*
from customer_with_varry c, table(c.addresses) a
where id = 1;
COLUMN_VALUE
-----------------------------------
2 State Street, Beantown, MA, 12345
select *
from table(
select addresses
where id = 1
);
COLUMN_VALUE
-----------------------------------
2 State Street, Beantown, MA, 12345
2.將table()函數應用於嵌套表
select a.*
from customer_with_nested_tabel c, table(c.addresses) a
where id = 1;
STREET CITY ST ZIP
-------------------------------------
2 State Street Beantown MA 12345
七.更改集合元素
1.更改變長數組元素
注意:只能作爲整體來修改
update customer_with_varry
set addresses = t_varray_address(
'ShengXia Streest, Shanghai, CA, 3346',
'ZuChongZhi Streest, Shanghai, CA, 8978'
)
where id = 1;
2.更改嵌套表元素
insert into table(
select addresses
from customer_with_nested_tabel
where id = 1
) values (
t_address('5 Main Streest', 'Uptonwn', 'NY', '55512')
);
update table(
select addresses
from customer_with_nested_tabel
where id = 1
) addr
set values(addr) =
t_address('ShengXia Streest', 'Shanghai', 'CA', '3346')
where value(addr) =
t_address('5 Main Streest', 'Uptonwn', 'NY', '55512');
delete from table(
select addresses
from customer_with_nested_tabel
where id = 1
)addr
where value(addr) =
t_address('ShengXia Streest', 'Shanghai', 'CA', '3346')
八.使用映射方法比較嵌套表的內容
注意:變長數組的類型不能直接比較
滿足以下三個條件,兩個嵌套表才相等:
- 兩個嵌套表具有相同的類型
- 兩個嵌套表具有相同的行數
- 兩個嵌套表的所有元素的值都相同
如果嵌套表是內置數據庫類型,那麼數據庫會自動比較嵌套表的內容。如果嵌套表的元素時用戶定義的對象類型,那麼需要提供映射函數。
create type t_address2 as object (
street varchar2(15),
city varchar2(15),
state char(2),
zip varchar2(5),
map member function get_string return varchar2
);
create type body t_address2 as
map member function get_string return varchar2 is
begin
return zip || ' '||state||' '||city||' '||street;
end get_string;
end;
使用submultiset of比較是否一個嵌套表的內容是另一個的子集
九.使用CAST()函數將集合從一種類型轉換爲另一種類型
1.使用CAST()函數將變長數組轉換爲嵌套表
select cast(cv.addresses as t_nested_table_address)
from customer_with_varry cv
where cv.id = 1;
2.使用CAST()函數將嵌套錶轉換爲變長數組
select cast(cv.addresses as customer_with_varry)
from t_nested_table_address cv
where cv.id = 1;