转载的
今天复习数据库的SQL，想着需要总结下各种数据库的SQL的不同点，供总结查阅，供别人参考！
- 返回的记录的数目
1. SQL Server 的语法：
SELECT TOP number|percent column_name(s)
FROM table_name
2. MySql的语法：
SELECT column_name(s)
FROM table_name
LIMIT number
3. Oracle的语法：
SELECT column_name(s)
FROM table_name
WHERE ROWNUM <= number
注意:oracle ROWNUM不支持">="
· SQL UNIQUE 约束
1. MySQL:
CREATE TABLE Persons
(
Id_P int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
UNIQUE(Id_P)
2. SQL Server / Oracle / MS Access:
CREATE TABLE Persons
(
Id_P int NOT NULL UNIQUE,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)
3. MySQL / SQL Server / Oracle / MS Access:
CREATE TABLE Persons
(
Id_P int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
CONSTRAINT uc_PersonID UNIQUE (Id_P,LastName)
)
· SQL UNIQUE Constraint on ALTER TABLE
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Persons
ADD UNIQUE (P_Id)
或
ALTER TABLE Persons
ADD CONSTRAINT uc_PersonID UNIQUE (P_Id,LastName)
- 撤销 UNIQUE 约束
1. MySql:
ALTER TABLE Persons
DROP INDEX uc_PersonID
2. SQL Server / Oracle / MS Access:
ALTER TABLE Persons
DROP CONSTRAINT uc_PersonID
这里只提供UNIQUE约束，PRIMARY KEY约束、FOREIGN KEY约束、CHECK约束类似。
· SQL AUTO INCREMENT 字段
1. MySql:
CREATE TABLE Persons
(
P_Id int NOT NULL AUTO_INCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
PRIMARY KEY (P_Id)
)
2. SQL Server:
CREATE TABLE Persons
(
P_Id int PRIMARY KEY IDENTITY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)
3.Access:
CREATE TABLE Persons
(
P_Id int PRIMARY KEY AUTOINCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)
4. Oracle:
CREATE SEQUENCE seq_person
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10
INSERT INTO Persons (P_Id,FirstName,LastName)
VALUES (seq_person.nextval,'Lars','Monsen')
- NULL 函数
1. SQL server/ MS Access
SELECT ProductName,UnitPrice*(UnitsInStock+ISNULL(UnitsOnOrder,0))
FROM Products
2. Oracle
SELECT ProductName,UnitPrice*(UnitsInStock+NVL(UnitsOnOrder,0))
FROM Products
3.MySql
SELECT ProductName,UnitPrice*(UnitsInStock+IFNULL(UnitsOnOrder,0))
FROM Products
或
SELECT ProductName,UnitPrice*(UnitsInStock+COALESCE(UnitsOnOrder,0))
FROM Products
作者: Dxx23
声明: 本文系JavaEye网站发布的原创文章，未经作者书面许可，严禁任何网站转载本文，否则必将追究法律责任！