SqlServer子查詢、高級

1. 子查詢：把一個結果集讓別人繼續分析查詢的就叫子查詢
2. 子查詢如果定義了別名，在查詢引用時，必須使用別名

3. --子查詢定義了別名,引用就必須用別名
   select id,n
   from Person,(select depname as n from Depment ) as d

   常用運算符：

4. in：表示對多個單列結果進行條件匹配

5. --in例子
   
   select name,age 
   from Person
   where Age in(select Age from Person where Age < 19)
   
   --any例子:與運算符結合使用,大於表示要大於查詢到的結果集
   
   select name,age
   from Person
   where Age <any(select Age from Person where Age < 19)

   exists

6. --exists:判斷是否為空，為空false，否則true
   
   select * from Person
   where exists(select * from Depment where id='002')
   
   
   select * from Person
   where exists(
   select * from Depment d where d.id = Person.DepID
   )

   將結果集直接在數據庫插入一張新表，多數據插入

   1. --數據量多插入數據：列必須前后對應
      
      create table person3(id int primary key,name varchar(30),age int, depid varchar(20))
      
      insert into person3( id,name,age,depid)
      select ID,Name,Age,DepID from person

      更新，刪除類似

7. Sql注入攻擊問題，采用參數化傳參形式可解決
8. 事務：保證數據原子性、一致性、隔離性、持久性
9. 開窗函數：可以對每一行結果都返回一個值，避免了group by必須分組的問題
   1. select count(*) over() from 表名

   2. select COUNT(*) over(partition by city) from shakerecode  參數意思是根據城市來分組顯示出城市的數量

10. 連接池：訪問數據庫時所產生的鏈接驗證成功后，當釋放連接對象時，數據庫就把此連接對象放到了連接池，下次使用時先從連接池找，如果連接池有這個連接對象直接使用，減少驗證等消耗。
    1. 打開數據庫連接對象的時間要正好，使用完連接對象要盡快釋放，這樣連接池的利用率高
    2. 連接字符串默認自動打開連接池，如果就想關閉連接池加語法pooling=false;
11. 子查詢分頁

12. --子查詢分頁
    --between (頁碼-1)*每頁條數+1   and  頁碼*每頁條數 
    select * from
    (
    select ROW_NUMBER() over(order by id) as num, * from Student
    ) t
    where t.num between (1-1)*10+1 and 1*10

     創建視圖、修改視圖分頁

go
create view vw_student
as
select * from
(
select ROW_NUMBER() over(order by id) as num, * from Student
) t
where t.num between (1-1)*10+1 and 1*10
go

--修改視圖

alter view vw_student
as
select * from
(
select ROW_NUMBER() over(order by id) as num, * from Student
) as t
go

select * from vw_student where num between 10 and 20

• 事務

--事務

--三個步驟：開始事務，提交事務，或者回滾事務

begin transaction

commit transaction

rollback transaction

set @@error  --記錄最近一次數據操作的錯誤，如果沒有錯誤默認是0

select @@error

• 存儲過程
• 存儲過程結合事務+變量+參數返回值，執行轉賬例子

go
create proc usp_BankToBank
@from nvarchar(10),
@to nvarchar(10),
@money money,
@issuccess int output
as
declare @myError int
set @myError = 0
begin
begin tran
update Bank set MoneyVal-=@money where ID = @from
set @myError = @myError+@@ERROR
update Bank set MoneyVal += @money where ID=@to
set @myError = @myError+@@ERROR
if @myError > 0
begin
set @issuccess = 0
rollback tran
end
else
begin
set @issuccess = 1
commit tran
end
end
go

declare @res int
exec usp_BankToBank '001','002',200,@res output
select @res

•  存儲過程分頁

create proc usp_StudentPage
@pageIndex int,
@pageCount int
as
begin
select * from
(
select ROW_NUMBER() over(order by id) as num,* from Student
) t
where t.num between (@pageIndex-1)*@pageCount + 1 and @pageIndex*@pageCount
end
go;

exec usp_StudentPage 2,20

•  觸發器

alter trigger tr_刪除觸發器 on bank
after
delete
as
insert into Bank(ID,moneyval)
select * from deleted;

• 獲取新增數據本身值

• -獲取最近一次插入數據的值
  
  insert into Bank(ID,MoneyVal) output inserted.* values('004',20)