1、MySQL 为关系型数据库(Relational Database Management System), 这种所谓的”关系型”可以理解为”表格”的概念, 一个关系型数据库由一个或数个表格组成

2、sql语句：

                   SELECT * FROM sdb_link 

                   SELECT link_id FROM sdb_link 

                   SELECT * FROM sdb_link where link_name=’外贸’  //WHERE 用于选择规定选择的标准

                   WHERE   操作符 > 、<、 = 、<> 、>= 、<=、BETWEEN、LIKE

                   SELECT DISTINCT orderlist FROM sdb_link   //DISTINCT 用于返回唯一不同的值

                   SELECT * FROM Persons WHERE FirstName=’Thomas’ AND LastName=’Carter’   //AND 条件都符合

                   SELECT * FROM Persons WHERE firstname=’Thomas’ OR lastname=’Carter’       // OR 只要有一个条件符合

                   SELECT Company, OrderNumber FROM Orders ORDER BY Company     //ORDER BY 语句用于根据指定的列对结果集进行排序。DESC 倒序   ASC 顺序

                   INSERT INTO sdb_link VALUES (104, 17, ‘测试17’, ‘http://www.baidu.com’,”,17,true,”,”,1)  //INSERT INTO 插入数据

                   INSERT INTO Persons (Lastname,Address) VALUES(‘Wilson’,’Champs-Elysees’)

                   UPDATE Person SET FirstName = ‘Fred’ WHERE LastName = ‘Wilson’      //UPDATE   更新一条数据

                   CREATE TABLE Persons(Id_P int,LastName varchar(255),FirstName varchar(255),Address varchar(255),City varchar(255))

                   DELETE FROM Person WHERE LastName = ‘Wilson’        //DELETE 删除一条数据

                   SELECT  * FROM sdb_link LIMIT 5  

                   SELECT  * FROM sdb_link WHERE link_id IN (1,2,5,6)  

                   SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2

                   SELECT link_id AS ID, link_name AS Name FROM sdb_link      //AS

                   SELECT sdb_link.link_id,sdb_jpush.id  FROM sdb_link,sdb_jpush     //查询多张表信息

                   SELECT sdb_link.link_id,sdb_jpush.id  FROM sdb_link,sdb_jpush WHERE sdb_link.link_id=sdb_jpush.id 

                   SELECT sdb_link.link_id,sdb_jpush.id FROM sdb_link INNER JOIN sdb_jpush ON sdb_link.link_id = sdb_jpush.id

                   SELECT sdb_link.link_id,sdb_jpush.id FROM sdb_link LEFT JOIN sdb_jpush ON sdb_link.link_id = sdb_jpush.id    //LEFT JOIN 关键字会从左表 (table_name1) 那里返回所有的行，即使在右表 (table_name2) 中没有匹配的行

                   SELECT sdb_link.link_id,sdb_jpush.id FROM sdb_link RIGHT JOIN sdb_jpush ON sdb_link.link_id = sdb_jpush.id    //RIGHT JOIN 关键字会从右表 (table_name1) 那里返回所有的行，即使在左表 (table_name2) 中没有匹配的行

                   SELECT column_name(s) FROM sdb_link UNION SELECT column_name(s) FROM sdb_jpush   //UNION 内部的 SELECT 语句必须拥有相同数量的列。列也必须拥有相似的数据类型。同时，每条 SELECT 语句中的列的顺序必须相同

                   SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo FROM Persons FULL JOIN Orders ON Persons.Id_P=Orders.Id_P ORDER BY Persons.LastName    // FULL JOIN  全连接

3、sql  函数