Net学习日记_SQL进阶_2

注意：

select  top 3 Name,Age,Gender from view_Student where group having order by id desc

     5     6        7        7       7           1      1                     2        3         4         8        8    8

在最终生成用户想要的数据之后，才进行排序，如果不得不排序，那么就尽可能把消耗减到最小。

系统变量

error 记录的是最后一个出现错误的地方的错误号（消息后面的数字）

事务里面必须用到这个error。

IF（）ELSE（）

条件表达式里面，可以使用一个只有一行一列的查询作为判断的一个根据
IF( (SELECT COUNT(id) FROM dbo.Student) >10)
BEGIN
PRINT '好多人啊'
END
ELSE
begin
PRINT '人好少啊'
END

 

触发器

触发器最难的是在与根据业务需求，写出触发器里面需要执行的sql语句。

触发器本生并不难。

After 和for 都是在增删改执行的时候执行另外的sql语句。

Instead of 是，取代原来的操作。

--创建一个新增触发器
CREATE TRIGGER tgforClassesOnInsert ON Classes
AFTER INSERT 
as
begin
PRINT '新增了一行数据'
--INSERT INTO log (操作的表，执行时间，哪个用户)
END
--创建一个删除触发器
CREATE TRIGGER tgforClassesOnDelete ON Classes
AFTER DELETE
as
begin
PRINT '删除了一行数据'
END
--创建一个修改触发器
CREATE TRIGGER tgForClassesOnUpdate ON Classes
AFTER UPDATE
as
begin
PRINT '修改了一行数据'
END

--*********FOR
CREATE TRIGGER tgclassupdate ON classes
FOR    update
as
begin
PRINT 'for的更新'
END
CREATE TRIGGER tgclassinsert ON classes
FOR    INSERT
as
begin
PRINT 'for的插入'
END
CREATE TRIGGER tgclassdelete ON classes
FOR    DELETE
as
begin
PRINT 'for的删除'
END

--************instead OF
CREATE TRIGGER tgclassesIinsert ON classes
instead OF INSERT
as
begin
PRINT 'instead ++ INSERT'
END
CREATE TRIGGER tgclassesIupdate ON classes
instead OF update
as
begin
PRINT 'instead ++ update'
END
CREATE TRIGGER tgclassesIdelete ON classes
instead OF delete
as
begin
PRINT 'instead ++ delete'
END

 

事务

储存过程

--大部分学生不及格，提分，直到一半学生及格为止
if exists(select * from sysobjects where [name]='usp_upGrade')
    drop proc usp_upGrade
go
create proc usp_upGrade
as
    begin
        declare @count int --记录总人数
        set @count = (select count(*) from score)
        while @count/2 < (select count(*) from score where english<60)
            begin
                update score set english= english+ 2 
            end
        update score set english = 100 where english> 100
    end
go

--带输入参数的存储过程
--题出难了，降低及格分数线
if exists(select * from sysobjects where [name]='usp_upGrade1')
    drop proc usp_upGrade1
go
create proc usp_upGrade1
    @pass float = 60
as
    begin
        declare @count int --记录总人数
        set @count = (select count(*) from score)
        while @count/2 < (select count(*) from score where english<@pass)
            begin
                update gradeInfo set grade = grade + 2 
            end
        update score set english = 100 where english> 100
    end

exec usp_upGrade1 80

--输出参数
if exists(select * from sysobjects where [name]='usp_upGrade2')
    drop proc usp_upGrade2
go
create proc usp_upGrade2
    @num int output,@pass float = 60
as
    begin
        set @num = 0
        declare @count int --记录总人数
        set @count = (select count(*) from gradeInfo)
        while @count/2 >= (select count(*) from gradeInfo where grade>=@pass)
            begin
                set @num = @num + 1
                update gradeInfo set grade = grade + 2 
            end
        update gradeInfo set grade = 100 where grade > 100
    end