01 SQL核心语句

在 sqlplus 中可以使用 ; 或 / 来执行一条 sql 语句, 但是 / 必须要换行, 个人感觉只有那些脚本啊什么的最后一般使用 / , 其他的都使用;

核心语句

SELECT

oracle 基于查询成本的优化器(cost-based optimizer, CBO) 用来产生实际的执行计划.  SQL 语句的执行顺序

5  select *

  from tablename

  where

  group by

  having

  order by

INSERT

直接介绍多表插入

   1:  insert all

   2:      when sum_orders < 10000 then

   3:          into small_customers

   4:      when sum_orders >= 10000 and sum_orders < 100000 then

   5:          into medium_customers

   6:      else

   7:          into large_customers

   8:  select customer_id, sum(order_total) sum_orders

   9:  from oe.orders

  10:  group by customer_id;

  11:   

  12:  -- 注意上例是仿照

  13:  insert into scott.bonus(ename, job, sal)

  14:  select ename, job, sal from scott.emp;

UPDATE

-- example 2 使用子查询作为修改的值

   1:  update employees2

   2:  set (salary, first_name) = ( select salary * 10, last_name

   3:                                   from employees

   4:                               where employees.employee_id = employees2.employee_id)

   5:  where department_id = 90;

DELETE

   1:  delete from (select * from employees2 where department_id = 90);

MERGE