Oracle Sql高级编程 第1章 SQL 基础

SELECT
语句

一个查询语句在逻辑上的处理方式可能会与实际物理处理过程不同。Oracle 基于查询成本的优化器用来产生实际的
执行计划。

查询语句的逻辑处理顺序

5	Select <column list>
1	from
1.1	from join on
2	where
3	group by
4	having
6	order by

可以把处理过程中的每一个步骤想象为生成一个临时的数据集。随着每个处理步骤的进行，这个数据集被不断的操作。

FROM

注意在处理联接语句时按下面的顺序进行:

交叉联接

内联接

外联接

一般，排序是查询过程中开销相当大的一个处理，尤其是当数据量很大时。

INSERT

INSERT

INTO

HR.JOBS (JOB_ID, JOB_TITLE, MIN_SALARY, MAX_SALARY)

VALUES

(
'IT_PM'
,
'Project Manager'

,
5000
,

11000
)

INSERT

INTO

SCOTT.BONUS

(ENAME, JOB, SAL)

SELECT

NAME
, JOB, SAL *

0.1

FROM

SCOTT.EMP;

INSERT

ALL

WHEN

SUM_ORDERS <

10000

THEN

INTO

SMALL_CUSTOMERS

WHEN

SUM_ORDERS >=

10000

AND

SUM_ORDERS <

100000

THEN

INTO

MEDIUM_CUSTOMERS

ELSE

INTO

LARGE_CUSTOMERS

SELECT

CUSTOMER_ID,

SUM
( ORDER_TOTAL) SUM_ORDERS

FROM

OE.ORDERS

GROUP

BY

CUSTOMER_ID;

UPDATE

UPDATE

EMPLOYEES

SET

SALARY = SALARY *

1.1

WHERE

DEPARTMENT_ID =

90
;

UPDATE

EMPLOYEES

SET

SALARY =

(

SELECT

EMPLOYEES2.SALARY

FROM

EMPLOYEES2

WHERE

EMPLOYEES2.EMPLID =

1
)

MERGE

MERGE

INTO

DEPT60_BONUSES B

USING

(
SELECT

EMPLID , SALARY, DEPTID

FROM

EMPLOYEES

WHERE

DEPTID =

60

) E

ON

(B.EMPLID = E.EMPLID)

WHEN

MATCHED

THEN

UPDATE

SET

B.BONUS_AMT = E.SALARY *

0.2

WHERE

B.BONUS_AMT =

0

DELETE

WHERE

( E.SALARY >

7500
)

WHEN

NOT

MATCHED

THEN

INSERT

(B.EMPLID, B.BONUS_AMT)

VALUES

(E.EMPLID, E.SALARY *

0.1
)

WHERE

(E.SALARY <

7500

);