自連線+非等值連線
自連線+group by = 遞迴集合
表是行的集合，面向集合
開銷較大
唯二重要的方法
case 自連線
sql語言 ： 面向集合的特性
有序對<>、無序對{}
--獲取可重排列(交叉連線 笛卡爾積) 3*3
select p1.name as name_1, p2.name as name_2
from products p1, product p2;
--獲取排列 a32 = 3*2
select p1.name as name_1, p2.name as name_2
from products p1, products p2
where p1.name <> p2.name;
--獲取組合c32 = 2*3 / 2
select p1.name as name_1, p2.name as name_2
from products p1, products p2
where p1.name > p2.name;
--獲取組合: 擴充套件程3列
select p1.name as name_1, p2.name as name_2, p3.name as name_3
from products p1, products p2, products as p3
where p1.name > p2.name
and p2.name > p3.name;
--關聯子查詢：對兩個擁有相同資料的集和進行的關聯操作
delete
from products p1
where rowid <
(select
max(p2.rowid)
)from products p2
where p1.name = p2.name
and p1.price = p2.price )
;--集合是sql唯一可以處理的資料結構
--刪除重複行（2）：非等值連線 **更常用**
delete
from products p1
where
exists
(select
*from products p2
where p1.name = p2.name
and p1.price = p2.price
and p1.rowid < p2.rowid )
;
--查詢同一家人住址不同
--尋找**相等的商品組合（+ distinct 避免出現重複行）
--自連線 + 非等值連線
select
distinct a1.name， a1.address
from addresses a1, addresses a2
where a1.family_id = a2.family_id
and a1.address <> a2.address ;
-- 用於查詢**相等但商品名稱不同的記錄的 sql 語句(distinct)
select
distinct p1.name, p1.price
from products p1, products p2
where p1.price = p2.price
and p1.name <> p2.name;
--關聯子查詢方法（作業）
select p1.name, p1.price
from products as p1
where p1.name <>
(select p2.name
from products as p2
where p1.price = p2.price)
不跳過之後的位次
--視窗函式
select name, price,
--跳過之後的位次，123336
rank(
)over
(order
by price desc
)as rank_1
--不跳過之後的位次，123334
dense_rank(
)over
(order
by price desc
)as rank_2
from products
--非等值自連線
--有幾個比自己大的再加一就是自己的排序
--排序從 1 開始。如果已出現相同位次，則跳過之後的位次
--去掉 +1 則從0排序；count(distinct p2.price)，則不跳過之後的位次。
select p1.name, p1.price,
(select
count
(p2.price)
from products p2
where p2.price > p1.price)+1
as rank_1
from products p1
order
by rank_1;
--排序：使用自連線
select p1.name,
max(p1.price)
as price,
count
(p2.name)+1
as rank_1
from products p1 left
outer
join products p2
on p1.price < p2.price
group
by p1.name
order
by rank_1;
--排序：使用內連線，結果沒有第一名
select p1.name,
max(p1.price)
as price,
count
(p2.name)+1
as rank_1
from products p1 inner
join products p2
on p1.price < p2.price
group
by p1.name
order
by rank_1;
select p1.name as name_1, p2.name as name_2
from products p1 products p2
where p1.name >= p2.name;
select district, name, price,
rank over
(partition
by district order
by price desc
)as rank_1
from districtproducts;
--關聯子查詢
select p1.district, p1.name,
p1.price,
(select
count
(p2.price)
from districtproducts p2
where p1.district = p2.district /* 在同乙個地區內進行比較 */
and p2.price > p1.price)+1
as rank_1
from districtproducts p1;
/* 練習題1-2-2：自連線 */
select p1.district, p1.name,
max(p1.price)
as price,
count
(p2.name)+1
as rank_1
from districtproducts p1 left
outer
join districtproducts p2
on p1.district = p2.district
and p1.price < p2.price
group
by p1.district, p1.name;
/* 練習題1-2-3：更新位次 */
--關聯子查詢
update districtproducts2 p1
set ranking =
(select
count
(p2.price)+1
from districtproducts2 p2
where p1.district = p2.district
and p2.price > p1.price)
;
--自連線
update districtproducts2
set ranking =
(select p1.ranking
from
(select district , name ,
rank(
)over
(partition
by district
order
by price desc
)as ranking
from districtproducts2) p1
where p1.district = districtproducts2.district
and p1.name = districtproducts2.name)
;
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