分类: Oracle
2011-01-24 09:52:26
用途:
从指定表中取出指定的列的数据
语法:
SELECT column_name(s) FROM table_name |
解释:
从数据库中选取资料列,并允许从一或多个资料表中,选取一或多个资料列或资料行。SELECT 陈述式的完整语法相当复杂,但主要子句可摘要为:
SELECT select_list
[ INTO new_table ]
FROM table_source
[ WHERE search_condition ]
[ GROUP BY group_by_expression ]
[ HAVING search_condition ]
[ ORDER BY order_expression [ ASC | DESC ] ]
例:
“Persons” 表中的数据有
LastName |
FirstName |
Address |
City |
Hansen |
Ola |
Timoteivn 10 |
Sandnes |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
Pettersen |
Kari |
Storgt 20 |
Stavanger |
选出字段名” LastName”、” FirstName” 的数据
SELECT LastName,FirstName FROM Persons |
返回结果:
LastName |
FirstName |
Hansen |
Ola |
Svendson |
Tove |
Pettersen |
Kari |
选出所有字段的数据
SELECT * FROM Persons |
返回结果:
LastName |
FirstName |
Address |
City |
Hansen |
Ola |
Timoteivn 10 |
Sandnes |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
Pettersen |
Kari |
Storgt 20 |
Stavanger |
Where
用途:
被用来规定一种选择查询的标准
语法:
SELECT column FROM table WHERE column condition value |
下面的操作符能被使用在WHERE中:
=,<>,>,<,>=,<=,BETWEEN,LIKE
注意: 在某些SQL的版本中不等号< >能被写作为!=
解释:
SELECT语句返回WHERE子句中条件为true的数据
例:
从” Persons”表中选出生活在” Sandnes” 的人
SELECT * FROM Persons WHERE City='Sandnes' |
"Persons" 表中的数据有:
LastName |
FirstName |
Address |
City |
Year |
Hansen |
Ola |
Timoteivn 10 |
Sandnes |
1951 |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
1978 |
Svendson |
Stale |
Kaivn 18 |
Sandnes |
1980 |
Pettersen |
Kari |
Storgt 20 |
Stavanger |
1960 |
返回结果:
LastName |
FirstName |
Address |
City |
Year |
Hansen |
Ola |
Timoteivn 10 |
Sandnes |
1951 |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
1978 |
Svendson |
Stale |
Kaivn 18 |
Sandnes |
1980 |
And & Or
用途:
在WHERE子句中AND和OR被用来连接两个或者更多的条件
解释:
AND在结合两个布尔表达式时,只有在两个表达式都为 TRUE 时才传回 TRUE
OR在结合两个布尔表达式时,只要其中一个条件为 TRUE 时,OR便传回 TRUE
例:
"Persons" 表中的原始数据:
LastName |
FirstName |
Address |
City |
Hansen |
Ola |
Timoteivn 10 |
Sandnes |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
Svendson |
Stephen |
Kaivn 18 |
Sandnes |
用AND运算子来查找"Persons" 表中FirstName为”Tove”而且LastName为” Svendson”的数据
SELECT * FROM Persons WHERE FirstName='Tove' AND LastName='Svendson' |
返回结果:
LastName |
FirstName |
Address |
City |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
用OR运算子来查找"Persons" 表中FirstName为”Tove”或者LastName为” Svendson”的数据
SELECT * FROM Persons WHERE firstname='Tove' OR lastname='Svendson' |
返回结果:
LastName |
FirstName |
Address |
City |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
Svendson |
Stephen |
Kaivn 18 |
Sandnes |
你也能结合AND和OR (使用括号形成复杂的表达式),如:
SELECT * FROM Persons WHERE (FirstName='Tove' OR FirstName='Stephen') AND LastName='Svendson' |
返回结果:
LastName |
FirstName |
Address |
City |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
Svendson |
Stephen |
Kaivn 18 |
Sandnes |
Between…And
用途:
指定需返回数据的范围
语法:
SELECT column_name FROM table_name WHERE column_name BETWEEN value1 AND value2 |
例:
“Persons”表中的原始数据
LastName |
FirstName |
Address |
City |
Hansen |
Ola |
Timoteivn 10 |
Sandnes |
Nordmann |
Anna |
Neset 18 |
Sandnes |
Pettersen |
Kari |
Storgt 20 |
Stavanger |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
用BETWEEN…AND返回LastName为从”Hansen”到”Pettersen”的数据:
SELECT * FROM Persons WHERE LastName BETWEEN 'Hansen' AND 'Pettersen' |
返回结果:
LastName |
FirstName |
Address |
City |
Hansen |
Ola |
Timoteivn 10 |
Sandnes |
Nordmann |
Anna |
Neset 18 |
Sandnes |
Pettersen |
Kari |
Storgt 20 |
Stavanger |
为了显示指定范围之外的数据,也可以用NOT操作符:
SELECT * FROM Persons WHERE LastName NOT BETWEEN 'Hansen' AND 'Pettersen' |
返回结果:
LastName |
FirstName |
Address |
City |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
Distinct
用途:
DISTINCT关键字被用作返回唯一的值
语法:
SELECT DISTINCT column-name(s) FROM table-name |
解释:
当column-name(s)中存在重复的值时,返回结果仅留下一个
例:
“Orders”表中的原始数据
Company |
OrderNumber |
Sega |
3412 |
W3Schools |
2312 |
Trio |
4678 |
W3Schools |
6798 |
用DISTINCT关键字返回Company字段中唯一的值:
SELECT DISTINCT Company FROM Orders |
返回结果:
Company |
Sega |
W3Schools |
Trio |
Order by
用途:
指定结果集的排序
语法:
SELECT column-name(s) FROM table-name ORDER BY { order_by_expression [ ASC | DESC ] } |
解释:
指定结果集的排序,可以按照ASC(递增方式排序,从最低值到最高值)或者DESC(递减方式排序,从最高值到最低值)的方式进行排序,默认的方式是ASC
例:
“Orders”表中的原始数据:
Company |
OrderNumber |
Sega |
3412 |
ABC Shop |
5678 |
W3Schools |
2312 |
W3Schools |
6798 |
按照Company字段的升序方式返回结果集:
SELECT Company, OrderNumber FROM Orders ORDER BY Company |
返回结果:
Company |
OrderNumber |
ABC Shop |
5678 |
Sega |
3412 |
W3Schools |
6798 |
W3Schools |
2312 |
按照Company字段的降序方式返回结果集:
SELECT Company, OrderNumber FROM Orders ORDER BY Company DESC |
返回结果:
Company |
OrderNumber |
W3Schools |
6798 |
W3Schools |
2312 |
Sega |
3412 |
ABC Shop |
5678 |
Group by
用途:
对结果集进行分组,常与汇总函数一起使用。
语法:
SELECT column,SUM(column) FROM table GROUP BY column |
例:
“Sales”表中的原始数据:
Company |
Amount |
W3Schools |
5500 |
IBM |
4500 |
W3Schools |
7100 |
按照Company字段进行分组,求出每个Company的Amout的合计:
SELECT Company,SUM(Amount) FROM Sales GROUP BY Company |
返回结果:
Company |
SUM(Amount) |
W3Schools |
12600 |
IBM |
4500 |
Having
用途:
指定群组或汇总的搜寻条件。
语法:
SELECT column,SUM(column) FROM table GROUP BY column HAVING SUM(column) condition value |
解释:
HAVING 通常与 GROUP BY 子句同时使用。不使用 GROUP BY 时,HAVING 则与 WHERE 子句功能相似。
例:
“Sales”表中的原始数据:
Company |
Amount |
W3Schools |
5500 |
IBM |
4500 |
W3Schools |
7100 |
按照Company字段进行分组,求出每个Company的Amout的合计在10000以上的数据:
SELECT Company,SUM(Amount) FROM Sales GROUP BY Company HAVING SUM(Amount)>10000 |
返回结果:
Company |
SUM(Amount) |
W3Schools |
12600 |
Join
用途:
当你要从两个或者以上的表中选取结果集时,你就会用到JOIN。
例:
“Employees”表中的数据如下,(其中ID为主键):
ID |
Name |
01 |
Hansen, Ola |
02 |
Svendson, Tove |
03 |
Svendson, Stephen |
04 |
Pettersen, Kari |
“Orders”表中的数据如下:
ID |
Product |
01 |
Printer |
03 |
Table |
03 |
Chair |
用Employees的ID和Orders的ID相关联选取数据:
SELECT Employees.Name, Orders.Product FROM Employees, Orders WHERE Employees.ID = Orders.ID |
返回结果:
Name |
Product |
Hansen, Ola |
Printer |
Svendson, Stephen |
Table |
Svendson, Stephen |
Chair |
或者你也可以用JOIN关键字来完成上面的操作:
SELECT Employees.Name, Orders.Product FROM Employees INNER JOIN Orders ON Employees.ID = Orders.ID |
INNER JOIN的语法:
SELECT field1, field2, field3 FROM first_table INNER JOIN second_table ON first_table.keyfield = second_table.foreign_keyfield |
解释:
INNER JOIN返回的结果集是两个表中所有相匹配的数据。
LEFT JOIN的语法:
SELECT field1, field2, field3 FROM first_table LEFT JOIN second_table ON first_table.keyfield = second_table.foreign_keyfield |
用”Employees”表去左外联结”Orders”表去找出相关数据:
SELECT Employees.Name, Orders.Product FROM Employees LEFT JOIN Orders ON Employees.ID = Orders.ID |
返回结果:
Name |
Product |
Hansen, Ola |
Printer |
Svendson, Tove |
|
Svendson, Stephen |
Table |
Svendson, Stephen |
Chair |
Pettersen, Kari |
|
解释:
LEFT JOIN返回”first_table”中所有的行尽管在” second_table”中没有相匹配的数据。
RIGHT JOIN的语法:
SELECT field1, field2, field3 FROM first_table RIGHT JOIN second_table ON first_table.keyfield = second_table.foreign_keyfield |
用”Employees”表去右外联结”Orders”表去找出相关数据:
SELECT Employees.Name, Orders.Product FROM Employees RIGHT JOIN Orders ON Employees.ID = Orders.ID |
返回结果:
Name |
Product |
Hansen, Ola |
Printer |
Svendson, Stephen |
Table |
Svendson, Stephen |
Chair |
解释:
RIGHT JOIN返回” second_table”中所有的行尽管在”first_table”中没有相匹配的数据。
Alias
用途:
可用在表、结果集或者列上,为它们取一个逻辑名称
语法:
给列取别名:
SELECT column AS column_alias FROM table |
给表取别名:
SELECT column FROM table AS table_alias |
例:
“Persons”表中的原始数据:
LastName |
FirstName |
Address |
City |
Hansen |
Ola |
Timoteivn 10 |
Sandnes |
Svendson |
Tove |
Borgvn 23 |
Sandnes |
Pettersen |
Kari |
Storgt 20 |
Stavanger |
运行下面的SQL:
SELECT LastName AS Family, FirstName AS Name FROM Persons |
返回结果:
Family |
Name |
Hansen |
Ola |
Svendson |
Tove |
Pettersen |
Kari |
运行下面的SQL:
SELECT LastName, FirstName FROM Persons AS Employees |
返回结果:
Employees中的数据有:
LastName |
FirstName |
Hansen |
Ola |
Svendson |
Tove |
Pettersen |
Kari |
Insert Into
用途:
在表中插入新行
语法:
插入一行数据
INSERT INTO table_name VALUES (value1, value2,....) |
插入一行数据在指定的字段上
INSERT INTO table_name (column1, column2,...) VALUES (value1, value2,....) |
例:
“Persons”表中的原始数据:
LastName |
FirstName |
Address |
City |
Pettersen |
Kari |
Storgt 20 |
Stavanger |
运行下面的SQL插入一行数据:
INSERT INTO Persons VALUES ('Hetland', 'Camilla', 'Hagabakka 24', 'Sandnes') |
插入后”Persons”表中的数据为:
LastName |
FirstName |
Address |
City |
Pettersen |
Kari |
Storgt 20 |
Stavanger |
Hetland |
Camilla |
Hagabakka 24 |
Sandnes |
运行下面的SQL插入一行数据在指定的字段上:
INSERT INTO Persons (LastName, Address) VALUES ('Rasmussen', 'Storgt 67') |
插入后”Persons”表中的数据为:
LastName |
FirstName |
Address |
City |
Pettersen |
Kari |
Storgt 20 |
Stavanger |
Hetland |
Camilla |
Hagabakka 24 |
Sandnes |
Rasmussen |
|
Storgt 67 |
|
Update
用途:
更新表中原有数据
语法:
UPDATE table_name SET column_name = new_value WHERE column_name = some_value |
例:
“Person”表中的原始数据:
LastName |
FirstName |
Address |
City |
Nilsen |
Fred |
Kirkegt 56 |
Stavanger |
Rasmussen |
|
Storgt 67 |
|
运行下面的SQL将Person表中LastName字段为”Rasmussen”的FirstName更新为”Nina”:
UPDATE Person SET FirstName = 'Nina' WHERE LastName = 'Rasmussen' |
更新后”Person”表中的数据为:
LastName |
FirstName |
Address |
City |
Nilsen |
Fred |
Kirkegt 56 |
Stavanger |
Rasmussen |
Nina |
Storgt 67 |
|
同样的,用UPDATE语句也可以同时更新多个字段:
UPDATE Person SET Address = 'Stien 12', City = 'Stavanger' WHERE LastName = 'Rasmussen' |
更新后”Person”表中的数据为:
LastName |
FirstName |
Address |
City |
Nilsen |
Fred |
Kirkegt 56 |
Stavanger |
Rasmussen |
Nina |
Stien 12 |
Stavanger |
Delete
用途:
删除表中的数据
语法:
DELETE FROM table_name WHERE column_name = some_value |
例:
“Person”表中的原始数据:
LastName |
FirstName |
Address |
City |
Nilsen |
Fred |
Kirkegt 56 |
Stavanger |
Rasmussen |
Nina |
Stien 12 |
Stavanger |
删除Person表中LastName为”Rasmussen”的数据:
DELETE FROM Person WHERE LastName = 'Rasmussen' |
执行删除语句后”Person”表中的数据为:
LastName |
FirstName |
Address |
City |
Nilsen |
Fred |
Kirkegt 56 |
Stavanger |
Create Table
用途:
建立新的资料表。
语法:
CREATE TABLE table_name ( column_name1 data_type, column_name2 data_type, ....... ) |
例:
创建一张叫“Person”的表,该表有4个字段"LastName", "FirstName", "Address", "Age":
CREATE TABLE Person ( LastName varchar, FirstName varchar, Address varchar, Age int ) |
如果想指定字段的最大存储长度,你可以这样:
CREATE TABLE Person ( LastName varchar(30), FirstName varchar(30), Address varchar(120), Age int(3) ) |
下表中列出了在SQL的一些数据类型:
Data Type |
Description |
integer(size) |
Hold integers only. The maximum number of digits are specified in parenthesis. |
decimal(size,d) |
Hold numbers with fractions. The maximum number of digits are specified in "size". The maximum number of digits to the right of the decimal is specified in "d". |
char(size) |
Holds a fixed length string (can contain letters, numbers, and special characters). The fixed size is specified in parenthesis. |
varchar(size) |
Holds a variable length string (can contain letters, numbers, and special characters). The maximum size is specified in parenthesis. |
date(yyyymmdd) |
Holds a date |
Alter Table
用途:
在已经存在的表中增加后者移除字段
语法:
ALTER TABLE table_name ADD column_name datatype ALTER TABLE table_name DROP COLUMN column_name |
注意:某些数据库管理系统不允许移除表中的字段
例:
“Person”表中的原始数据:
LastName |
FirstName |
Address |
Pettersen |
Kari |
Storgt 20 |
在Person表中增加一个名为City的字段:
ALTER TABLE Person ADD City varchar(30) |
增加后表中数据如下:
LastName |
FirstName |
Address |
City |
Pettersen |
Kari |
Storgt 20 |
|
移除Person表中原有的Address字段:
ALTER TABLE Person DROP COLUMN Address |
移除后表中数据如下:
LastName |
FirstName |
City |
Pettersen |
Kari |
|
Drop Table
用途:
在数据库中移除一个数据表定义及该数据表中的所有资料、索引、触发程序、条件约束及权限指定。
语法:
DROP TABLE table_name |
Create Database
用途:
建立新的数据库.
语法:
CREATE DATABASE database_name |
Drop Database
用途:
移除原有的数据库
语法:
DROP DATABASE database_name |
聚集函数 count
用途:
传回选取的结果集中行的数目。
语法:
SELECT COUNT(column_name) FROM table_name |
例:
“Persons”表中原始数据如下:
Name |
Age |
Hansen, Ola |
34 |
Svendson, Tove |
45 |
Pettersen, Kari |
19 |
选取记录总数:
SELECT COUNT(Name) FROM Persons |
执行结果:
3 |
sum
用途:
以表达式传回所有值的总和,或仅 DISTINCT 值。SUM 仅可用于数值资料行。已忽略 Null 值。
语法:
SELECT SUM(column_name) FROM table_name |
例:
“Persons”表中原始数据如下:
Name |
Age |
Hansen, Ola |
34 |
Svendson, Tove |
45 |
Pettersen, Kari |
19 |
选取”Persons”表中所有人的年龄总和:
SELECT SUM(Age) FROM Persons |
执行结果:
98 |
选取”Persons”表中年龄超过20岁的人的年龄总和:
SELECT SUM(Age) FROM Persons WHERE Age>20 |
执行结果:
79 |
avg
用途:
传回选取的结果集中值的平均值。已忽略 Null 值。
语法:
SELECT AVG(column_name) FROM table_name |
例:
“Persons”表中原始数据如下:
Name |
Age |
Hansen, Ola |
34 |
Svendson, Tove |
45 |
Pettersen, Kari |
19 |
选取”Persons”表中所有人的平均年龄:
SELECT AVG(Age) FROM Persons |
执行结果:
32.67 |
选取”Persons”表中年龄超过20岁的人的平均年龄:
SELECT AVG(Age) FROM Persons WHERE Age>20 |
执行结果:
39.5 |
max
用途:
传回选取的结果集中值的最大值。已忽略 Null 值。
语法:
SELECT MAX(column_name) FROM table_name |
例:
“Persons”表中原始数据如下:
Name |
Age |
Hansen, Ola |
34 |
Svendson, Tove |
45 |
Pettersen, Kari |
19 |
选取”Persons”表中的最大年龄:
SELECT MAX(Age) FROM Persons |
执行结果:
45 |
min
用途:
传回选取的结果集中值的最小值。已忽略 Null 值。
语法:
SELECT MIN(column_name) FROM table_name |
例:
“Persons”表中原始数据如下:
Name |
Age |
Hansen, Ola |
34 |
Svendson, Tove |
45 |
Pettersen, Kari |
19 |
选取”Persons”表中的最小年龄:
SELECT MIN(Age) FROM Persons |
执行结果:
19 |
算术函数 abs
用途:
传回指定数值表达式 (Numeric Expression) 的绝对正值。
语法:
ABS(numeric_expression) |
例:
ABS(-1.0) ABS(0.0) ABS(1.0) |
执行结果:
1.0 0.0 1.0 |
ceil
用途:
传回大于等于给定数值表达式的最小整数。
语法:
CEIL(numeric_expression) |
例:
CEIL(123.45) CEIL(-123.45) |
执行结果:
124.00 -123.00 |
floor
用途:
传回小于或等于给定数值表达式的最大整数。
语法:
FLOOR(numeric_expression) |
例:
FLOOR(123.45) FLOOR(-123.45) |
执行结果:
123.00 -124.00 |
cos
用途:
在指定表达式中传回指定角度 (以弪度为单位) 的三角余弦值的数学函数。
语法:
COS(numeric_expression) |
例:
COS(14.78) |
执行结果:
-0.599465 |
cosh
用途:
传回以弧度为单位的角度值,其余弦为指定的 float 表达式,也称为反余弦。
语法:
COSH(numeric_expression) |
例:
COSH(-1) |
执行结果:
3.14159 |
sin
用途:
以近似的数值 (float) 表达式传回给定角度 (以弧度) 之三角正弦函数 (Trigonometric Sine)。
语法:
SIN(numeric_expression) |
例:
SIN(45.175643) |
执行结果:
0.929607 |
sinh
用途:
传回以弪度为单位的角度,其正弦为指定的 float 表达式 (也称为反正弦)。
语法:
SINH(numeric_expression) |
例:
SINH(-1.00) |
执行结果:
-1.5708 |
tan
用途:
传回输入表达式的正切函数。
语法:
TAN(numeric_expression) |
例:
TAN(3.14159265358979/2) |
执行结果:
1.6331778728383844E+16 |
tanh
用途:
传回以弪度为单位的角度,其正切为指定的 float 表达式 (也称为反正切)。
语法:
TANH(numeric_expression) |
例:
TANH(-45.01) |
执行结果:
-1.54858 |
exp
用途:
传回给定的 float 表达式的指数 (Exponential) 值。
语法:
EXP(numeric_expression) |
例:
EXP(378.615345498) |
执行结果:
2.69498e+164 |
log
用途:
传回给定的 float 表达式之自然对数。
语法:
LOG(numeric_expression) |
例:
LOG(5.175643) |
执行结果:
1.64396 |
power
用途:
传回给定表达式指定乘幂的值。
语法:
POWER(numeric_expression,v) |
例:
POWER(2,6) |
执行结果:
64 |
sign
用途:
传回给定的表达式之正 (+1)、零 (0) 或负 (-1) 号。
语法:
SIGN(numeric_expression) |
例:
SIGN(123) SIGN(0) SIGN(-456) |
执行结果:
1 0 -1 |
sqrt
用途:
传回给定表达式的平方。
语法:
SQRT(numeric_expression) |
例:
SQRT(10) |
执行结果:
100 |
原文地址:
http://www.blogjava.net/lusm/archive/2007/06/27/126669.html