• 深入学习之mysql(五)连接查询


    深入学习Mysql(五)连接查询
    1、准备数据库:
    CREATE DATABASE IF NOT EXISTS `db_book2` DEFAULT CHARACTER SET UTF8;
     
    USE `db_book2`;
     
    DROP TABLE IF EXISTS `t_book`;
     
    CREATE TABLE `t_book` (
    `id` INT(11) PRIMARY KEY AUTO_INCREMENT,
    `bookName` VARCHAR(20) DEFAULT NULL,
    `price` DECIMAL(6,2) DEFAULT NULL,
    `author` VARCHAR(20) DEFAULT NULL,
    `bookTypeId` INT(11) DEFAULT NULL
    ) ENGINE=INNODB DEFAULT CHARSET=UTF8;
     
    INSERT INTO `t_book` VALUES (NULL,'Java编程思想','100.00','埃史尔',1),(NULL,'Struts2权威指南','80.00','李刚',1),(NULL,'三剑客','70.00','大仲马',2),(NULL,'生理学(第二版)','24.00','刘先国',3);
     
    DROP TABLE IF EXISTS `t_booktype`;
     
    CREATE TABLE `t_booktype` (
    `id` INT(11) PRIMARY KEY AUTO_INCREMENT,
    `bookTypeName` VARCHAR(20) DEFAULT NULL
    ) ENGINE=INNODB DEFAULT CHARSET=UTF8;
     
    INSERT INTO `t_booktype`(`id`,`bookTypeName`) VALUES (1,'计算机类'),(2,'文学类'),(3,'教育类');
     
     
    2、连接查询:连接查询是将2个或者2个以上的表按照某个条件连接起来,从中选取需要的数据。
    2.1、内连接:内连接可以查询2个或者2个以上的表;
    例:查询t_book表中的编号,作者,书名和t_bookType表的类别名称:
     
    SELECT t1.id,t1.author,t1.bookName,t2.bookTypeName FROM t_book t1,t_booktype t2 WHERE t1.bookTypeId=t2.id;
    +----+-----------+----------------------+--------------+
    | id | author | bookName | bookTypeName |
    +----+-----------+----------------------+--------------+
    | 1 | 埃史尔 | Java编程思想 | 计算机类 |
    | 2 | 李刚 | Struts2权威指南 | 计算机类 |
    | 3 | 大仲马 | 三剑客 | 文学类 |
    | 4 | 刘先国 | 生理学(第二版) | 教育类 |
    +----+-----------+----------------------+--------------+
    4 rows in set (0.02 sec)
    2.2.外链接查询:
    外链接可以查询出某一张表中的所有信息;
    SELECT 属性名列表FROM 表名1 LEFT|RIGHT JOIN 表名2 ON 表名1.属性名1=表名2.属性名2;
    2.2.1:左连接查询:可以查询出表名1的所有记录,而表名2中只能查出匹配的记录:
    例:以左外连接查询t_book 中的所有信息:
    SELECT * FROM t_book t1 LEFT JOIN t_bookType t2 ON t1.bookTypeId = t2.id;

    SELECT * FROM t_book t1 LEFT JOIN t_bookType t2 ON t1.bookTypeId = t2.id;
    +----+----------------------+--------+--------------+------------+------+--------------+
    | id | bookName | price | author | bookTypeId | id | bookTypeName |
    +----+----------------------+--------+--------------+------------+------+--------------+
    | 1 | Java编程思想 | 100.00 | 埃史尔 | 1 | 1 | 计算机类 |
    | 2 | Struts2权威指南 | 80.00 | 李刚 | 1 | 1 | 计算机类 |
    | 3 | 三剑客 | 70.00 | 大仲马 | 2 | 2 | 文学类 |
    | 4 | 生理学(第二版) | 24.00 | 刘先国 | 3 | 3 | 教育类 |
    | 5 | 大主宰 | 20.00 | 天蚕土豆 | 4 | NULL | NULL |
    +----+----------------------+--------+--------------+------------+------+--------------+
    5 rows in set (0.00 sec)
     
    2.2.2右连接查询:
    SELECT * FROM t_book t1 LEFT JOIN t_bookType t2 ON t1.bookTypeId = t2.id;
    +------+----------------------+--------+-----------+------------+----+--------------+
    | id | bookName | price | author | bookTypeId | id | bookTypeName |
    +------+----------------------+--------+-----------+------------+----+--------------+
    | 1 | Java编程思想 | 100.00 | 埃史尔 | 1 | 1 | 计算机类 |
    | 2 | Struts2权威指南 | 80.00 | 李刚 | 1 | 1 | 计算机类 |
    | 3 | 三剑客 | 70.00 | 大仲马 | 2 | 2 | 文学类 |
    | 4 | 生理学(第二版) | 24.00 | 刘先国 | 3 | 3 | 教育类 |
    +------+----------------------+--------+-----------+------------+----+--------------+
    4 rows in set (0.00 sec)
    2.2.3:多条件查询:
    例: 查询t_book表中编号,作者,书名和t_bookType表的的类别名称,价格在20-30之间的记录
     
    mysql> SELECT t1.id,t1.author,t1.bookName,t1.price,t2.bookTypeName FROM t_book t1,t_booktype t2 WHERE t1.bookTypeId=t2.id AND price BETWEEN 20 AND 30;
    +----+-----------+----------------------+-------+--------------+
    | id | author | bookName | price | bookTypeName |
    +----+-----------+----------------------+-------+--------------+
    | 4 | 刘先国 | 生理学(第二版) | 24.00 | 教育类 |
    +----+-----------+----------------------+-------+--------------+
    1 row in set (0.00 sec)
    2.2.4:自连接查询
    例:以自连接方式查询t_book表中作者不是天蚕土豆的所有记录:
    SELECT t1.* FROM t_book t1,t_book t2 WHERE t1.id=t2.id AND t2.author<>'天蚕土豆';
    mysql> SELECT t1.* FROM t_book t1,t_book t2 WHERE t1.id=t2.id AND t2.author<>'天蚕土豆';
    +----+----------------------+--------+-----------+------------+
    | id | bookName | price | author | bookTypeId |
    +----+----------------------+--------+-----------+------------+
    | 1 | Java编程思想 | 100.00 | 埃史尔 | 1 |
    | 2 | Struts2权威指南 | 80.00 | 李刚 | 1 |
    | 3 | 三剑客 | 70.00 | 大仲马 | 2 |
    | 4 | 生理学(第二版) | 24.00 | 刘先国 | 3 |
    +----+----------------------+--------+-----------+------------+
    4 rows in set (0.00 sec)
     
     
     
     
     
     
     
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  • 原文地址:https://www.cnblogs.com/itor/p/7063850.html
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