笔记02：高级查询

keer — Sun, 17 Aug 2008 05:27:00 GMT

keer 2008-08-17 13:27 发表评论

笔记01：查询

keer — Sun, 27 Jul 2008 03:10:00 GMT

1. 更改用户

alter user scott account unlock;

2. 表结构

desc emp;

名称                                      是否为空? 类型
----------------------------------------- -------- -------------------
EMPNO                                     NOT NULL NUMBER(4)
ENAME                                              VARCHAR2(10)
JOB                                                VARCHAR2(9)
MGR                                                NUMBER(4)
HIREDATE                                           DATE
SAL                                                NUMBER(7,2)
COMM                                               NUMBER(7,2)
DEPTNO                                             NUMBER(2)

3. dual表

SQL> select 2*3 from dual;

2*3
----------
6

SQL> select sysdate from dual;

SYSDATE
----------
17-8月 -08

4. 改变标题

select sal*12 "Anuual Sal" from emp；

Anuual Sal
----------
9600
19200
15000
35700
15000

5. 字段连接

select ename ||'character' from emp

ENAME||'CHARACTER'
------------------
SMITHcharacter
ALLENcharacter
WARDcharacter
JONEScharacter
MARTINcharacter
BLAKEcharacter

/* 若字符串中本来就有单引号，则用两个单引号来替代一个单引号 */
select ename ||'charac''ter' from emp

ENAME||'CHARAC''TER'
-------------------
SMITHcharac'ter
ALLENcharac'ter
WARDcharac'ter
JONEScharac'ter
MARTINcharac'ter
BLAKEcharac'ter

6. distinct 去除重复行或重复组合

select distinct deptno from emp

DEPTNO
------
10
20
30

select distinct job from emp

JOB
-----------
ANALYST
CLERK
MANAGER
PRESIDENT
SALESMAN

/*将deptno与job重复的组合去掉*/
select distinct deptno, job from emp

DEPTNO    JOB
----------------------
10    CLERK
10    MANAGER
10    PRESIDENT
20    ANALYST
20    CLERK
20    MANAGER
30    CLERK
30    MANAGER
30    SALESMAN

7. where 语句

=
>
<
<>
>=
<=
between and
in (a,b,c)
is (null)
is not (null)
like
not like
.
.
.

select ename from emp where ename  like  '_A%'

ENAME
------
WARD
MARTIN
JAMES

/* 如果字符串中本来就带有%, 则加转义字符 */
select ename from emp where ename  like  '%/%%'

ENAME
------
W%%D
MART%N
J%AMES

/* 可指定别的符号为转移字符，以替代默认的反斜杠 */
select ename from emp where ename  like  '%$%%' escape '$'

8. 排序

select * from dept order by deptno desc

DEPTNO    DNAME    LOC
-------------------------------------
40    OPERATIONS    BOSTON
30    SALES    CHICAGO
20    RESEARCH    DALLAS
10    ACCOUNTING    NEW YORK

select ename , sal, deptno from emp order by deptno, ename desc

ENAME    SAL    DEPTNO
----------------------
MILLER    1300.00    10
KING    5000.00    10
CLARK    2450.00    10
SMITH    800.00    20
SCOTT    3000.00    20
JONES    2975.00    20
FORD    3000.00    20
ADAMS    1100.00    20
WARD    1250.00    30
TURNER    1500.00    30
MARTIN    1250.00    30
JAMES    950.00    30
BLAKE    2850.00    30
ALLEN    1600.00    30

总结如下：

select ename ,sal*12 "Annual Sal" from emp
where ename not like '_A%' and sal>800
order by sal desc

ENAME    Annual Sal
------------------
KING    60000
SCOTT    36000
FORD    36000
JONES    35700
BLAKE    34200
CLARK    29400
ALLEN    19200
TURNER    18000
MILLER    15600
ADAMS    13200

keer 2008-07-27 11:10 发表评论

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