结构化查询语句

Posted 2020-09-23 树的种子

By TreeDream

基本表的定义，修改，删除简单查询单表查询连接查询等值与非等值查询外连接查询复合条件查询自身连接查询嵌套查询数据更新插入数据修改数据删除数据视图创建视图查询视图更新视图删除视图

基本表的定义，修改，删除

建表考虑列名，数据类型，列级完整性，表级完整性（参照性约束）

create table Salvaging
(
    prj_num char(8) primary key,
    prj_name varchar(50),
    start_date datetime,
    end_date datetime,
    prj_status bit,
);
?
create table Stock
(
    mat_num char(8) primary key,
    mat_name varchar(50) not null,
    speci varchar(20) not null,
    warehouse char(20),
    amount int,
    unit decimal(18,2),
    total as(amount*unit),
    check(mat_num like ‘[m][0-9][0-9][0-9]‘),
);
?
create table Out_stock
(
    prj_num char(8),
    mat_num char(8),
    amount int,
    get_date datetime default getdate(),
    department char(20),
    primary key (prj_num,mat_num),
    foreign key(prj_num) references Salvaging(prj_num),
    foreign key(mat_num) references Stock(mat_num),
);
?
alter table Salvaging add prj_director varchar(10);
alter table Salvaging drop column prj_director
?
drop table Salvaging

 

简单查询

单表查询

select prj_name 项目名称,start_date 开始日期,end_date 结束日期,DATEDIFF(day,start_date,end_date) 抢修天数
from Salvaging

 

select *
from Stock
where unit>=50 and unit<=100 --条件

 

in集合

select mat_num,speci,amount,warehouse
from Stock
where warehouse not in (‘供电局1#仓库‘,‘供电局2#仓库‘)

 

字符匹配

select *
from Stock
where mat_name like ‘__绝缘%‘

 

NULL值(is)

select *
from Stock
where unit is null

 

排序：只能对最后的查询结果排序

select *
from Stock
where mat_name=‘护套绝缘电线‘
order by unit desc  --默认从低到高(asc),desc从高到底

 

聚集函数

select MAX(amount),min(amount),avg(amount)
from Out_stock
where mat_num = ‘m001‘

 

分组

select prj_num 项目号,count(*) 物资种类
from Out_stock
group by prj_num

 

select prj_num 项目号,count(*) 物资种类
from Out_stock
group by prj_num
having count(*)>=2

 

连接查询

等值与非等值查询

等值 与非等值根据连接谓词

广义笛卡尔积不带谓词，没有意义；

自然连接：在等值连接的基础上，去除重复列

select Salvaging.prj_num,Salvaging.prj_name,mat_num,amount,get_date,end_date,department
from Salvaging,Out_stock
where Salvaging.prj_num = Out_stock.prj_num

 

外连接查询

连接操作中，如果有一个关系没有与之对应，就不会有输出，但是也丢失了另一个关系的基本情况，解决方案是外连接

外连接：左外连接，右外连接，全外连接

select Salvaging.prj_num,Salvaging.prj_name,mat_num,amount,get_date,end_date,department
from Salvaging left outer join Out_stock on (Salvaging.prj_num = Out_stock.prj_num)

 

复合条件查询

select distinct Salvaging.prj_num,Salvaging.prj_name
from Salvaging,Out_stock,Stock
where Salvaging.prj_num = Out_stock.prj_num and Out_stock.mat_num = Stock.mat_num and Stock.mat_name=‘护套绝缘电线‘

 

自身连接查询

select A.prj_num
from Out_stock A,Out_stock B
where A.prj_num = B.prj_num and A.mat_num = ‘m001‘ and B.mat_num = ‘m002‘

 

嵌套查询

带谓词in的嵌套查询（子查询往往是一个集合）

select Stock.mat_name,speci,amount
from Stock
where warehouse in (        -- = 亦可
        select warehouse
        from Stock
        where speci = ‘BVV-120‘ and mat_name = ‘护套绝缘电线‘
    )

 

/*
select Stock.mat_num,Stock.mat_name
from Salvaging,Out_stock,Stock
where Salvaging.prj_name=‘观澜站光缆抢修‘ and Salvaging.prj_num = Out_stock.prj_num and Out_stock.mat_num = Stock.mat_num
*/
?
select mat_num,mat_name
from Stock
where mat_num in (
    select mat_num
    from Out_stock
    where prj_num in (
        select prj_num
        from Salvaging
        where prj_name = ‘观澜站光缆抢修‘
    )
)

 

带比较运算符的嵌套查询

select mat_num,mat_name
from Stock s1
where amount > (
    select avg(amount) 
    from Stock s2
    where s2.warehouse = s1.warehouse
)

 

带any或all谓词的嵌套查询

select mat_name,speci,amount
from Stock
where warehouse <> ‘供电局1#仓库‘ and amount < ALL (
    select amount
    from stock
    where warehouse = ‘供电局1#仓库‘
)

 

带exists谓词的嵌套查询

select prj_name
from Salvaging
where exists (
    select*
    from Out_stock
    where prj_num = Salvaging.prj_num and mat_num = ‘m001‘
)

 

sql中没有全称量词，把全称量词转换为存在量词

--查询被所有工程使用过了的物资——没有一个工程没有使用过他
select mat_name,speci
from Stock
where not exists (
    select*
    from Salvaging
    where not exists (
        select*
        from Out_stock
        where mat_num = Stock.mat_num and prj_num = Salvaging.prj_num
    )
)

 

数据更新

插入数据

insert
into Salvaging
values (‘20110011‘,‘观澜站电缆接地抢修‘,‘2011-2-3 0:00:00‘,‘2011-2-5 12:00:00‘,1)

 

插入查询结果

insert
into Prj_cost
select prj_num,sum(out_stock.amount*unit)
from Out_stock,Stock
where Out_stock.mat_num = stock.mat_num
group by prj_num

 

修改数据

update Stock
set unit = 44.5
where mat_num = ‘m020‘

 

删除数据

delete
from Out_stock
where prj_num = ‘20110001‘ and mat_num = ‘m001‘

 

视图

• 视图是数据库数据的特定子集。可以禁止所有用户访问数据库表，而要求用户只能通过视图操作数据，这种方法可以保护用户和应用程序不受某些数据库修改的影响。

• 视图是抽象的，他在使用时，从表里提取出数据，形成虚的表。 不过对他的操作有很多的限制 。

创建视图

create view s1_stock
as
select mat_num,mat_name,speci,amount,unit
from Stock
where warehouse = ‘供电局1#仓库‘

 

查询视图

--像基本表一样查询视图
select *
from s1_stock

 

更新视图

--insert,delete
update s1_stock
set amount = 100
where mat_num = ‘m001‘

 

 

删除视图

drop view s1_stock