oracle-DML-2

1.update 语句

update  table set  [column,column......] where  column =''

示例： update   customers

set   cust_credit_limit = 20000

where   cust_id = 2789;

2.delete 语句

delete from table where  条件

示例; delete from customers

where cust_state_province = 'QT';

备注；truncate customers 也可以删除该表的所有记录，但是它在出错不允许回滚的

3.数据排序

order by

示例: select cust_id,cust_state_province, cust_credit_limit

from customers

where cust_credit_limit = 15000

and cust_state_province  in ('QT','CT')

order by cust_state_province ,cust_id ;

备注：oracle 默认的是按照升序排序，如果需要降序就 要在排序字段后面添加desc

示例：select cust_id ,cust_state_province,cust_credit_limit

from  customers

where cust_credit_limit =15000

and cust_state_province in  ('UT','CT')

order by cust_state_province ,cust_id desc

4.group by

group by 主要是分组 来进行求和 或者其它运算

示例：select prod_subcategory,avg(amout_sold)

from sales s ,products p

where s.prod_id = p.prod_id

and prod_category = 'Electronics'

group by prod_subcategory ;

5.having

在对group by 操作的使用having 字句可以限制返回的组

示例：select prod_subcategory,avg(amout_sold)

from sales s ,products p

where s.prod_id = p.prod_id

and prod_category = 'Electronics'

group by prod_subcategory

having avg(amout_sold) > 300;

6.子查询

sql 一个强大功能就是创建子查询，即查询中嵌套查询。这一功能使得基于另一结果或者其他结果集进行查询成为可能

示例：

select prod_id ,prod_name ,prod_category

from products

where  prod_list_price  =

(

select  max(prod_list_price) from products

);

7:集合操作

union 返回两表中无任何重复的所有行

示例：select * from x

union

select *from y

union all 返回两表中所以行（包含重复）

示例:select * from x

union all

select *from y

intersect 返回两表中都存在的行

示例:select * from x

intersect

select *from y