oracle 第05章 SQL语句

2015-10-12

目录

一、连接命令

　　1.$ sqlplus

　　2.SQL> conn

二、SELECT语句

　　1.简单查询

　　2.WEHRE子句

　　3.别名

　　4.算术运算符+ - * /

　　5.DISTINCT关键字

　　6.连接运算符||

　　7.单行函数

　　7.1字符型
　　　　LOWER
　　　　UPPER
　　　　INITCAP
　　　　CONCAT
　　　　SUBSTR
　　　　INSTR
　　　　LENGTH
　　　　LPAD|RPAD
　　7.2数值型
　　　　TRIM
　　　　REPLACE
　　　　ROUND
　　　　TRUNC
　　　　MOD
　　7.3日期型
　　　　SYSDATE
　　　　MONTHS_BETWEEN
　　　　ADD_MONTHS
　　　　NEXT_DAY
　　　　LAST_DAY
　　8.空值函数
　　　　IS NULL
　　　　IS NOT NULL
　　　　NVL,NVL2
　　　　NULLIF
　　　　COALESCE

　　9.条件表达式

　　　　CASE..WHEN..END

　　　　DECODE

　　10.分组函数

　　　　AVG

　　　　SUM

　　　　MAX

　　　　MIN　

　　　　COUNT

　　　　GROUP BY子句

　　　　HAVING 子句

三、INSERT语句

四、UPDATE语句

五、DELETE语句

一、连接命令
sqlplus 用户名/密码 [as 角色]
sqlplus /nolog 空用户，密码nolog登录
sqlplus sys/oracle as sysdba 用户sys，密码oracle，角色sysdba
sqlplus system/oracle 用户system，密码oracle
sqlplus scott/oracle 用户scott，密码oracle

SQL> conn 用户名/密码 [as 角色];
以sytem用户登录，解锁scott账户，并重置scott密码
SQL> conn system/oracle;
Connected.
SQL> alter user scott identified by oracle account unlock;

User altered.

再以scott用户登录
SQL> conn scott/oracle;
Connected.

二、SELECT语句
SELECT *|｛[DISTINCI] column | expression [alias],.....｝
FROM table;

1.简单查询

SQL> select * from dept;

切换到sytem用户登录，并查看scott用户的表dept
SQL> conn system/oracle;
Connected.

查看失败
SQL> select * from dept;
select * from dept
*
ERROR at line 1:
ORA-00942: table or view does not exist

查看成功
SQL> select * from scott.dept;

再切换回scott用户，查看dept表的某几列
SQL> conn scott/oracle
Connected.

SQL> select dname,loc from dept;

SQL> select dname,loc,deptno from dept;

2.where子句
SQL> select * from dept where loc = 'CHICAGO';

SQL> select * from dept where deptno < 30;

3.别名

双引号只作为列别名或表名，单引号是字符串。

SQL> select empno,ename,job,mgr,sal from emp;

SQL> select empno,ename employee_name,sal as salary,deptno "deptmentnumber" from emp;

4.算术运算符
SQL> select ename,sal*12 from emp where job = 'MANAGER';

SQL> select ename,sal*12+1000 from emp where job = 'MANAGER';

5.DISTINCI关键字
SQL> select job from emp;

SQL> select distinct job from emp;

6.连接运算符||
SQL> select ename,job,sal from emp;

SQL> select ename || ' is a '||job||' and 1month salary is :'|| sal as "the imployees's information" from emp;

7.单行函数

小写函数
LOWER(column|expression) 
SQL> select lower('Structured Query Language') from dual;

大写函数

UPPER(column|expression) 

SQL> select upper('Structured Query Language') from dual;

首字母大写函数

INITCAP(column|expression) 
SQL> select initcap('structured query language') from dual;

字符串连接函数

CONCAT(column1|expression1,column2|expression2)

SQL> select concat ('Structured Query Language', ' is easy to learn!') from dual;

SQL> select concat(ename,hiredate) "emp_name,hiredate" from emp;

子串函数

SUBSTR(column|expression,m[,n]) 
SQL> select substr('structured query language',12) from dual;

子串位置函数

INSTR(column|expression,'string',[,m],[n]) 
SQL> select instr('structured query language','query') from dual;

 字符串长度函数

LENGTH(column|expression)
SQL> select length('structured query language') from dual;

左|右填充函数
LPAD|RPAD(column|expression,n,'string') 
SQL> select LPAD(sal,10,'*') from emp where sal > 1500;

SQL> select RPAD(sal,10,'*') from emp where sal > 1500;

字符截断函数

TRIM(leading|trailing|both,trim_character FROM 'source_string') 
SQL> select trim('S' from 'SQL is an easy DatabaseS languageS') from dual;

替换函数

REPLACE(text,search_string,replacement_string) 
SQL> select replace('sql is an easy Database language','sql','Structured Query Language') from dual;

四舍五入函数

ROUND(column|expression,n) 
SQL> select round(32.1515,3) from dual;

SQL> select round(32.1515,-1) from dual;

数字截断函数

TRUNC(column|expression,n) 
SQL> select trunc(32.1515,3) from dual;

SQL> select trunc(32.1515,-1) from dual;

求余函数

MOD(m,n) 
SQL> select mod(1000,500) from dual;

SQL> select mod(100,500) from dual;

当前日期函数

SYSDATE 
SQL> select sysdate from dual;

SQL> select sysdate + 7 ,sysdate - 7 from dual;

SQL> select sysdate + 20/25 from dual;

SQL> select sysdate +1/25 from dual;

SQL> select to_date('06-JUN-16') - sysdate from dual;

月差函数

MONTHS_BETWEEN(date,date) 
SQL> select months_between('06-JUN-10','06-JUN-09') from dual;

SQL> select months_between('06-JUN-09','06-JUN-10') from dual;

加月函数

ADD_MONTHS(date,n) 
SQL> select sysdate from dual;

SQL> select add_months(sysdate,5) from dual;

下周几日期函数

NEXT_DAY(date,'string') 
SQL> select next_day(sysdate,'Saturday') from dual;

月末日期函数

LAST_DAY(date) 
SQL> select last_day(sysdate) from dual;

空值处理函数IS NULL,IS NOT NULL,NVL,NVL2,NULLIF,COALESCE
SQL> col empno for 9999;
SQL> col sal for 9999;
SQL> col comm for 9999;
SQL> col mgr for 9999;

只有salsman的comm非空
SQL> select empno,ename,job,mgr,hiredate,sal,comm from emp order by job;

查询comm = null 匹配不到结果
SQL> select empno,ename,job,mgr,hiredate,sal,comm from emp where comm = null;

no rows selected

查询comm is null 的记录
SQL> select empno,ename,job,mgr,hiredate,sal,comm from emp where comm is null;

查询comm is not null 的记录
SQL> select empno,ename,job,mgr,hiredate,sal,comm from emp where comm is not null;

NVL(expr1,expr2)空值转换函数
如果expr1的值为NULL，则返回expr2的值，否则返回expr1的值。

使用NVL函数计算sal的查询
SQL> select ename,sal,comm,sal+nvl(comm,0) from emp;

不使用NVL函数计算sal+comm的查询
SQL> select ename,sal,comm,sal+comm from emp;

NVL2(expr1,expr2,expr3) 空值转换函数2
如果expr1的值为NULL，则返回expr3的值，否则返回expr2的值。

使用NVL2函数计算sal+comm的查询
SQL> select ename,sal,comm,nvl2(comm,sal+comm,sal) from emp;

NULLIF(expr1,expr2) 表达式比较函数
如果expr1=expr2，则返回NULL，否则返回expr1的值

SQL> select ename,length(ename) "expr1",job,length(job) "expr2",nullif(length(ename),length(job)) "comparision_result" from emp;

COALESCE(expr1,expr2,...,exprn)空值转换函数3
返回从expr1到exprn中第一个不为NULL的表达式exprx的值

SQL> select ename "Employ_name",job,coalesce(comm,1) "Comm" from emp order by job;

CASE表达式
双引号只作为列别名或表名，单引号是字符串。
SQL> select ename,job,sal,
2 case job when 'salesman' then 1.2*sal
3 when 'manager' then 1.3*sal
4 when 'analyst' then 1.5*sal
5 else sal end "Last Salary"
6 from emp
7 order by job;

select ename,job,sal,case job when 'salesman' then 1.2*sal when 'manager' then 1.3*sal when 'analyst' then 1.5*sal else sal end "Last Salary" from emp order by job;

DECODE函数
SQL> select ename,job,sal,
2 decode(job,'salesman',1.2*sal,
3 'manger',1.3*sal,
4 'analyst',1.5*sal,
5 sal)
6 Last_Salary
7 from emp
8 order by job;

select ename,job,sal,decode(job,'salesman',1.2*sal,'manger',1.3*sal,'analyst',1.5*sal,sal) Last_Salary from emp order by job;

分组函数

AVG、SUM、MAX、MIN、COUNT
SQL> select avg(sal) "avg_sal" ,sum(sal) "total_sal" from emp;

SQL> select avg(sal),sum(sal),max(sal),min(sal),count(sal) from emp;

SQL> select hiredate from emp;

SQL> select max(hiredate),min(hiredate) from emp;

max、min既可用于数值型数据，也可用于字符型数据。

SQL> select count(*) from emp;

SQL> select count(distinct job) from emp;

GROUP BY 子句
SQL> select job,avg(sal),sum(sal) from emp group by job;

ORDER BY 子句
SQL> select job,avg(sal),sum(sal) from emp group by job order by sum(sal);

分组函数嵌套
SQL> select max(avg(sal)),min(avg(sal)) from emp group by job;

HAVING子句
SQL> select job,avg(sal) from emp having avg(sal)>2000 group by job;

SQL> select job,avg(sal) from emp having avg(sal)>2000 group by job order by avg(sal);

二、INSERT语句
INSERT INTO tablename [(column [,column ...])]
VALUES (value [,value ...])

INSERT INTO tablename [(column [,column ...])]
SELECT column [,column ...]
FROM another_tablename
WHERE clause

SQL> select * from dept;

SQL> desc dept;

SQL> insert into dept (deptno,dname,loc) values (60,'manager','new york');

1 row created.

SQL> select * from dept;

SQL> insert into dept(deptno,dname) values(70,'audit');

1 row created.

SQL> select * from dept;

三、UPDATE语句
UPDATE tablename
SET column = value [, column = value, ...]
[WHERE condition];

SQL> select * from dept;

SQL> update dept set loc = 'new york' where deptno = 70; 

1 row updated.

SQL> select * from dept;

四、DELETE语句
DELETE [FROM] tablename
[WHERE condition];

SQL> delete from dept where deptno = 60;

1 row deleted.

参考资料

[1] 林树泽.Oracle 11g R2 DBA操作指南[M].北京：清华大学出版社，2013

[2] Oracle数据库语句大全

[3] Oracle 复习知识点

[4] oracle常用sql查询语句部分集合(图文)

[5] oracle SQL命令大全

[6] sql语句百例之Oracle

[7] oracle基本操作sql语句

[8] 浅谈从Oracle数据库中取出10条数据的Select语句与SQL Server、MySQL的区别