009 identity 视图 分页

/*
时间：2020/09/13
功能：
    一 identity
    二 视图
    三 分页
*/   

一 identity

-- identity
create table student2
(
    student_id int primary key,
    student_name nvarchar(200) not null
)

insert into student2 values(1, '张三')
insert into student2 values(2, '李四')
insert into student2 values(3, '王五')

select * from student2

insert into student2(student_name) values('赵六')    -- error

create table student3
(
    student_id int primary key identity(100, 5),
    student_name nvarchar(200) not null
)

insert into student3 values('李四')
insert into student3 values('王五')

select * from student3

insert into student3 values(1, '张三') -- error
insert into student3(student_name) values('张三')

delete from student3 
    where student_name = '张三'
insert into student3 values('赵六')

二 视图

-- 求平均工资最高部门编号和部门平均工资
-- SQL Server
select top 1 deptno, avg(sal)
    from emp
    group by deptno
    order by avg(sal) desc

-- 通用SQL语句
select *
    from (
        select deptno, avg(sal) "avg_sal"
        from emp
        group by deptno
)"E"    -- 小表全部信息
where "E"."avg_sal" = (
select max("T"."avg_dept")
    from(
        select deptno, avg(sal) "avg_dept"
            from emp
            group by deptno
            ) "T"
)    -- 部门最高平均工资


-- 视图用法
create view v$_emp_1
as
    select deptno, avg(sal) "avg_sal"
        from emp
        group by deptno

select * 
    from v$_emp_1
    where avg_sal = (
        select max(avg_sal)
            from v$_emp_1
)

三 分页

-- 分页查询
-- 查询工资最高的员工信息，排序前三
select top 3 *
    from emp
    order by sal desc

-- 查询工资最高的员工信息，排序前4-6
select top 3 *
    from emp
    where empno not in
        (
            select top 3 empno
                from emp
                order by sal desc
        )
    order by sal desc

-- 查询工资最高的员工信息，排序前7-9
select top 3 *
    from emp
    where empno not in
        (
            select top 6 empno
                from emp
                order by sal desc
        )
    order by sal desc

-- 查询工资最高的员工信息，排序前10-12
select top 3 *
    from emp
    where empno not in
        (
            select top 9 empno
                from emp
                order by sal desc
        )
    order by sal desc


假设每页显示n条记录, 当前要显示第m页。
表名是A, 主键是A_id。
m n
1 0
2 3
3 6
4 9

select top n *
    from A
    where A_id not in 
    (
        select top (m-1)*n A_id
            from emp 
    )