sql必知必会

检索单列
select pro_id
form products；
检索多列
select pro_id,pro_name,pro_price
form products；
检索所有列
select *
form products;　

按单列排序
select pro_name
from products
order by pro_name;
按多列排序
select pro_name,pro_id,pro_price
from products
order by pro_price,pro_name;
按位置排序(select清单中的相对位置)
selcet pro_id,pro_price,pro_name
from products
order by 2,3;
指定排序方向(默认为升序asc,降序为desc)
select pro_id,pro_name,pro_price
from products
order by pro_price desc,pro_name

检查单个值
select pro_name,pro_price
from products
where pro_price = 10;
不匹配检查
select vend_id,pro_name
from products
where vend_id != ‘Dl001’
范围值检查
select pro_price,pro_name
from products
where pro_price between 5 and 10;
空值检查(NULL)
select pro_name
from products
where pro_price is null;

= 等于 
!= <> 不等于 
< 小于 
<= 小于等于 
!< 不小于
> 大于
>= 大于等于
!> 不大于
between 在两个值之间
is null 为空值 
and 与
or 或
in 在
not 非
() 用括号表示优先级

使用and or ()操作符
select pro_name,pro_price
from products
where (vend_id ='dl001' or vend_id='bs001') and pro_price > 10;
使用 in 操作符
select pro_name,pro_price
from products
where vend_id in ('dl001','sa001')
order by pro_name;
使用not 操作符
select pro_name
from products
where not vend_id = 'dl001'
order by pro_name;

使用百分号%匹配多个字符(acess使用*)
select pro_name,pro_id
from products
where pro_name like 'fish%'; 开头为fish的字符串
where pro_name like '%fish%'; 中间为fish
使用下划线 _ 匹配单个字符串
select pro_name,pro_id
from products
where pro_name like '_fish';
使用方括号[]
select cust_contact
from customers
where cust_contact like '[jm]%'
order by cust_contact;
取反 [^jm] ---access使用 [!jm]

字段（filed）
拼接（concatenate）将值连结到一起构成单个值(使用+或||)
select vend_name + '('+vend_country+')'
///mysql 使用 select contact(vend_name,'(',vend_country,')')
from venders
order by vend_name; 
使用函数去除空格 rtrim() trim() ltrim()
select rtrim(vend_name) + '('+rtrim(vend_country)+')'
from venders
order by vend_name; 
使用别名
select rtrim(vend_name) + '('+rtrim(vend_country)+')' as vned_titile
from venders
order by vend_name; 
执行算术计算(+ - * /)
select pro_id,quantity,pro_price,quantity*pro_price as expanded_price
from products
where order_num = 2008;

文本处理函数
左边left()
长度length() len() datalenth()
小写lower()
右边right()
大写upper() ucase()--acess
发音soundex()

soundex()

select cust_name,cust_contact
from customers
where soundex(cust_contact)=soundex('micheal green');

SQL server 和Sybase
select order_num
from orders
where datepart(yy,order_date)=2004;

Access
select order_num
from orders
where datepart(yyyy,order_date)=2004;

PostgreSQL
select order_num
from orders
where date_part(year,order_date)=2004;

常用数值函数
abs() 绝对值
cos()
exp() 指数值
pi()
sin()
sqrt() 平方根
tan()

聚集函数 ---返回一列中单个值
avg()
count()
max()
min()
sum()

案例　　
avg
select avg(pro_price) as avg_price
from products;

count
select count(*) as num_cust 所有行
from customers;
select count(cust_email) as num_cust 非空行
from customers;

distinct相同的值不计算
select avg(distinct pro_price) as avg_price
from products;

分组数据
select vend_id,count(*) as num_prods
from products
group by vend_id;相同的id将合并为一组
hanving
select vend_id,count(*) as num_prods
from products
where pro_price >=4
group by vend_id
having count(*)>=2;

分组排序
select order_num,count(*) as items
from orders;
group by order_num
having count(*) >=3
order by items,order_num;

acess不能使用别名
order by count(*),order_num;

子句顺序
selsect 返回的表达列
from 检索数据表来源
where 行级过滤
group by 分组说明
having 组级过滤 
order by 排序

子句中只能用一个select语句
select cust_name,cust_contact
from customers
where cust_id in （select cust_id

　　　　　　　　　　from ordersitems

　　　　　　　　　　where order_num in (select order_num

　　　　　　　　　　　　　　　　　　　　　from orderitems

　　　　　　　　　　　　　　　　　　　　　where pro_id='rga001'));

栗子
select vend_name,prod_name,prod_name
from vendors,products
where vendors.vend_id=products.vend_id;

内部联结（等值联结）
selsect cust_name,cust_dontact
from customers as c,orders as o,orderitems as oi
where c.cust_id = o.cust_id
　　　 and oi.order_num=o.order_num
　　　 and pro_id='rhano1';

普通方法
select cust_id,cust_name,cust_contact
from customers
where cust_name=(select cust_name
　　　　　　　　　　from customers
　　　　　　　　　　where cust_contact='jim jones');
自然联结方法
select c1.cust_id,c1.cust_name,c1.cust_contact
from customers as c1,customers as c2
where c1.cust_name = c2.cust_name
　　　 and c2.cust_contact = 'jim jones';
注意:otacle 中没有as 方法，使用时只需去掉as

select c.* o.order_num, oorder_date,oi.pro_id,oi.quantity,oi.item_price
from customers as c,orders as o,orderitems as oi
where c.cust_id= o.cust_id
          and oi.order_num=o.order_num
          and pro-id='rgan01';

内部联结
select customers.cust_id,orders.order_num
from customers,orders
where orders.cust_id =* customers.cust_id; 右边每行
where orders.cust_id *= customers.cust_id; 左边每行　

unioin案例
select cust_name,cust-contact,cust_email
from customers
where cust_state in ('il','in','mi')
union
select cust_name,cust_contact,cust_email
from customers
where cust_name = 'funall';

插入一行（不安全）
插入新行到表，没有的值为null
insert into customers
values('1005','ss','dfds',null,null); 

插入一行（安全）
insert into customers(cust_id,cust_contact,cust_name)
values('2313',null,'sss');

从表导入到一个新表
insert into customers(cust_id,cust_contact,cust_email)
select cust_id,cust_contact,cust_email
from custnew;

（db2不支持）
select *
into custcopy
from customers;

mysql 和oracle
create table cystcopy as
select *
from customers;

更新特定行
update customers
set cust_email='sdsdf'
where cust_id='asd';

更新多行
update customers
set cust_email='sdsdf'
　　cust_contact='ds'
where cust_id='asd';

更行所有行
删除行
delete from customers
where cust_id='2131';

creae table products
(pro_id char(10) not null,
vend_id char(10) not null,
pro_name decimal(8,2) not null,
pro_price integer not null default 1,
pro_desc varchar(100) null
);

使用默认值为日期
access now()
db2 current_date
mysql current_date()
oracle sysdate
postgreSQL current_date
sql sever getdate()
sybase getdate()　

增加行
alter tabel vendors
add vend_phone char(20);　

删除行
alter table vendors
drop column vend_phone;

删除表
drop table cust;

创建
create view prodouctscustomers as 
select cust_name,cust_contact,pro_id
from customers,orders,orderitems
where customers.cust_id=orders.cust_id
and orderitems.order_num=orders.order_num;

使用
select cust_name,cust_contact
from productcustomers
where pro_id='rag';

删除
drop view viewname;

执行存储过程
execute addnewproduct('jts01','sd',6.0,'sdfsdf')
执行 存储过程名 传入参数

创建存储过程

create procedure maillinglistcount
--listcount参数从存储过程里返回一个数字
(listcount out number) 
is 
begin　　　　　　　　　　　　
--存储过程开始
　　select * from customers
　　where not cust_email is null;
　　listcount := sql%rowcount;
end;　　　　　　　　　　　　　
--存储过程结束

SQL server
begin transaction
.....
commit transaction

MySQL
start transaction

PostgreSQL
begin;

delete insert update　

MySQL oracle
--保留点
savepoint delete1;
--回退
rollback to delete1;

sql server 和Sybase
save transaction delete1;
rollback transaction delete1;