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  • 各种数据库的SQL的不同点

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    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)
    
    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
    
     
    
     
    
    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!

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  • 原文地址:https://www.cnblogs.com/muyoushui/p/1946386.html
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