column_name(s) 数据库表中所有列的名称,column_name是一个列名称
1、SELECT(基本查询语句)
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1. SELECT DISTINCT Company, OrderNumber FROM Orders ORDER BY Company, OrderNumber DESC//降序
2. SELECT DISTINCT Company, OrderNumber FROM Orders ORDER BY Company, OrderNumber ASC//默认,升序
2、INSERT INTO(插入语句)
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1. INSERT INTO 表名称 VALUES (值1, 值2,....)//插入完整的一行数据
2. INSERT INTO table_name (列1, 列2,...) VALUES (值1, 值2,....)//插入一行中的某些数据
3、UPDATE(更新语句)
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1. UPDATE 表名称 SET 列名称 = 新值,列名称 = 新值,... WHERE 列名称 = 某值//一次性的更新多个属性值,用逗号隔开即可
4、DELETE(删除语句)
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1. DELETE FROM 表名称 WHERE 列名称 = 值
5、TOP(取出前n行数据)
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1. SELECT TOP number|percent column_name(s) FROM table_name//SQL Server
2. SELECT column_name(s) FROM table_name LIMIT number//MY SQL
3. SELECT column_name(s) FROM table_name WHERE ROWNUM <= number//ORACLE
6、IN(判断是否在集合中)
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1. SELECT column_name(s) FROM table_name WHERE column_name IN (value1,value2,...)
7、BETWEEN...AND(会选取介于两个值之间的数据范围。这些值可以是数值、文本或者日期。)
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1. SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2
8、SQL Alias(为属性或者表取别名)
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1. SELECT YHB.name FROM user AS YHB WHERE name LIKE '%员%';
2. SELECT LastName AS Family, FirstName AS Name FROM Persons
9、SQL JOIN(表连接,分全连接-内连接-外连接)
(1)INNER JOIN 返回两个表符合查询条件的所有值的组合
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1. SELECT column_name(s) FROM table_name1 INNER JOIN table_name2 ON table_name1.column_name=table_name2.column_name//等价于
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1. SELECT column_name(s) FROM table_name1,table_name2 WHERE table_name1.column_name=table_name2.column_name
(2)OUTER INNER (返回符合查询条件的两表的组合,并且还包含左表[LEFT INNER]或者右表[RIGHT INNER]的所有数据)
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1. SELECT column_name(s) FROM table_name1 LEFT JOIN table_name2 ON table_name1.column_name=table_name2.column_name//LEFT INNER
2. SELECT column_name(s) FROM table_name1 RIGHT JOIN table_name2 ON table_name1.column_name=table_name2.column_name//RIGHT INNER
10、SELECT INTO (从一个表中选取数据,然后把数据插入另一个表中。常用于创建表的备份复件或者用于对记录进行存档)
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1. SELECT * INTO new_table_name [IN externaldatabase] FROM old_tablename//可以生成到其他数据库中
11、CREATE DATABASE(建立数据库)
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1. CREATE DATABASE database_name
12、CREATE TABLE(创建新的表结构)
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1. CREATE TABLE Persons
2. (
3. Id_P int NOT NULL PRIMARY KEY,
4. LastName varchar(255),
5. FirstName varchar(255),
6. Address varchar(255),
7. City varchar(255)
8. )
13、FOREIGN KEY(设置外键)
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1. CREATE TABLE Orders
2. (
3. O_Id int NOT NULL,
4. OrderNo int NOT NULL,
5. Id_P int,
6. PRIMARY KEY (O_Id),
7. FOREIGN KEY (Id_P) REFERENCES Persons(Id_P)
8. )
14、DROP(删除表结构)
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1. DROP TABLE 表名称,表名称...//删除多个表
15、ALTER TABLE(修改表结构,如插入一列,删除一列,修改数据类型等)
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1. ALTER TABLE table_name ADD column_name datatype//加一列
2. ALTER TABLE table_name DROP COLUMN column_name//删除一列
3. ALTER TABLE table_name MODIFY COLUMN column_name datatype//改变一列的数据类型
16、NULL(IS NULL判断属性为空,IS NOT NULL判断属性不为空)
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1. SELECT LastName,FirstName,Address FROM Persons WHERE Address IS NULL
2. SELECT LastName,FirstName,Address FROM Persons WHERE Address IS NOT NULL
17、基本的函数
(1)AVG(求平均值)
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1. SELECT AVG(OrderPrice) AS OrderAverage FROM Orders
(2)SUM(求和)
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1. SELECT SUM(OrderPrice) AS OrderTotal FROM Orders
(3)COUNT(求行数)
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1. SELECT COUNT(column_name) FROM table_name
(4)MAX(取最大值)
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1. SELECT MAX(column_name) FROM table_name
(5)MIN(取最小值)
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1. SELECT MIN(column_name) FROM table_name
(6)GROUP BY
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1. SELECT u_id ,SUM(score) FROM score GROUP BY u_id HAVING u_id=1
(7)UCASE (函数把字段的值转换为大写)
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1. SELECT UCASE(column_name) FROM table_name
(8)LCASE (函数把字段的值转换为小写)
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1. SELECT LCASE(column_name) FROM table_name
(9)ROUND (函数用于把数值字段舍入为指定的小数位数)
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1. SELECT ROUND(column_name,decimals) FROM table_name//decimals指定保留的小数的位数,例如设置为0,则返回的数值没有小数部分
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