1.1 SELECT基本语法:
Select * |{[distinct]colum|expression [alias],…} from table;
1.2 查询当前用户所有在用的表及视图:
HR@ORA11GR2>select * from tab;
TNAME TABTYPE CLUSTERID
------------------------------ ------- ----------
BIN$QVpuz+vXGO3gUwEAAH/YAA==$0 TABLE
BIN$QX3Co/ONIBTgUwEAAH9Xiw==$0 TABLE
BIN$QXf2P63XEXzgUwEAAH8s7A==$0 TABLE
BIN$QXf2P63YEXzgUwEAAH8s7A==$0 TABLE
BIN$QXf2P63aEXzgUwEAAH8s7A==$0 TABLE
1.3 查看表的结构定义
HR@ORA11GR2>desc employees;
Name Null? Type
----------------------------------------------------- -------- ------------------------------------
EMPLOYEE_ID NOT NULL NUMBER(6)
FIRST_NAME VARCHAR2(20)
LAST_NAME NOT NULL VARCHAR2(25)
EMAIL NOT NULL VARCHAR2(25)
PHONE_NUMBER VARCHAR2(20)
HIRE_DATE NOT NULL DATE
JOB_ID NOT NULL VARCHAR2(10)
SALARY NUMBER(8,2)
COMMISSION_PCT NUMBER(2,2)
MANAGER_ID NUMBER(6)
DEPARTMENT_ID NUMBER(4)
1.4 查看表中所有数据
HR@ORA11GR2>select * from departments;
DEPARTMENT_ID DEPARTMENT_NAME MANAGER_ID LOCATION_ID
------------- ------------------------------ ---------- -----------
10 Administration 200 1700
20 Marketing 201 1800
30 Purchasing 114 1700
40 Human Resources 203 2400
50 Shipping 121 1500
60 IT 103 1400
1.5 查看表中指定列的数据
HR@ORA11GR2>select first_name,last_name,employee_id from employees;
FIRST_NAME LAST_NAME EMPLOYEE_ID
-------------------- ------------------------- -----------
Steven King 100
Neena Kochhar 101
Lex De Haan 102
Alexander Hunold 103
Bruce Ernst 104
David Austin 105
1.6 显示某一列的唯一值
HR@ORA11GR2>select distinct first_name from employees;
FIRST_NAME
--------------------
Ellen
Mozhe
Hermann
Alberto
Britney
1.7sql语句中的加、减、乘、除运算
1)数值型字段的加、减、乘、除运算
HR@ORA11GR2>select first_name,salary,salary+1000,salary-1000,salary*2,salary/2 from employees where first_name='Sarath';
FIRST_NAME SALARY SALARY+1000 SALARY-1000 SALARY*2 SALARY/2
------------ ---------- ----------- ----------- ---------- ----------
Sarath 7000 8000 6000 14000 3500
2)日期型字段进行加减(日期型字段不能乘除)
HR@ORA11GR2>select hire_date,hire_date-1,hire_date+1 from employees where first_name='Sarath';
HIRE_DATE HIRE_DATE-1 HIRE_DATE+1
------------------- ------------------- -------------------
2006-11-03 00:00:00 2006-11-02 00:00:00 2006-11-04 00:00:00
1.8null的检索
注:null值无法用=或<>来进行判断,只允许用is null和is not null来进行判断
HR@ORA11GR2>select count(*) from employees where commission_pct is null;
COUNT(*)
----------
72
HR@ORA11GR2>select count(*) from employees where commission_pct is not null;
COUNT(*)
----------
35
1.9 NULL的计算
注:NULL值与任何值四则运算后,其结果均为NULL。
HR@ORA11GR2>select last_name,commission_pct,commission_pct+200,commission_pct-200,commission_pct*2 from employees;
LAST_NAME COMMISSION_PCT COMMISSION_PCT+200 COMMISSION_PCT-200 COMMISSION_PCT*2
------------------------- -------------- ------------------ ------------------ ----------------
OConnell
Grant
Whalen
Hartstein
Russell .4 200.4 -199.6 .8
LAST_NAME COMMISSION_PCT COMMISSION_PCT+200 COMMISSION_PCT-200 COMMISSION_PCT*2
------------------------- -------------- ------------------ ------------------ ----------------
Partners .3 200.3 -199.7 .6
Errazuriz .3 200.3 -199.7 .6
Cambrault .3 200.3 -199.7 .6
Zlotkey .2 200.2 -199.8 .4
Tucker .3 200.3 -199.7 .6
1.10 SQL连接符与单引号的使用<可用来编写批量脚本>
HR@ORA11GR2>select 'select * from '||tname||';' from tab;
'SELECT*FROM'||TNAME||';'
---------------------------------------------
select * from BIN$QVpuz+vXGO3gUwEAAH/YAA==$0;
select * from BIN$QX3Co/ONIBTgUwEAAH9Xiw==$0;
select * from BIN$QXf2P63XEXzgUwEAAH8s7A==$0;
select * from BIN$QXf2P63YEXzgUwEAAH8s7A==$0;
select * from BIN$QXf2P63aEXzgUwEAAH8s7A==$0;
select * from BIN$QXf2P63bEXzgUwEAAH8s7A==$0;
select * from BIN$QXf2P63dEXzgUwEAAH8s7A==$0;
select * from BIN$QXs3u7LlHOfgUwEAAH94zw==$0;
select * from COUNTRIES;
select * from COURSE;
select * from DEPARTMENTS;
1.11 Aslias别名
在SELECT选取字段后可接 as 或者空格,来替代字段别名,如果还有空格、特殊字符以及大小写需要用双引号
HR@ORA11GR2>select 'xiaoming' as "Name",1 id from dual;
Name ID
-------- ----------
xiaoming 1
1.12 distinct 删除重复值
HR@ORA11GR2>select distinct manager_id from employees;
MANAGER_ID
----------
100
123
120
121
147
205
108
148
149
201
MANAGER_ID
----------
102
101
114
124
145
146
103
122
HR@ORA11GR2>select distinct manager_id,department_id from employees;
MANAGER_ID DEPARTMENT_ID
---------- -------------
100 30
147 80
90
108 100
149
101 40
100 90
102 60
103 60
114 30
100 50