MYSQL之连接查询

CREATE TABLE `t_book` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`bookName` varchar(20) DEFAULT NULL,
`price` decimal(6,2) DEFAULT NULL,
`author` varchar(20) DEFAULT NULL,
`bookTypeId` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
);

insert  into `t_book`(`id`,`bookName`,`price`,`author`,`bookTypeId`) values (1,'Java编程思想','100.00','埃史尔',1),(2,'Java从入门到精通','80.00','李钟尉',1),(3,'三剑客','70.00','大仲马',2),(4,'生理学(第二版)','24.00','刘先国',4);

CREATE TABLE `t_booktype` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`bookTypeName` varchar(20) DEFAULT NULL,
PRIMARY KEY (`id`)
);

insert  into `t_booktype`(`id`,`bookTypeName`) values (1,'计算机类'),(2,'文学类'),(3,'教育类');

查询两个类别的笛卡尔乘积
SELECT * FROM t_book,t_bookType;

内连接查询，查询ID相同的所有信息
SELECT * FROM t_book,t_bookType WHERE t_book.bookTypeId=t_bookType.id;

内连接查询，查询ID相同的书名、作者、书类别
SELECT bookName,author,bookTypeName FROM t_book,t_bookType WHERE t_book.bookTypeId=t_bookType.id;

给表加个别名，t_book设为tb，t_bookType设为tby
SELECT tb.bookName,tb.author,tby.bookTypeName FROM t_book tb,t_bookType tby WHERE tb.bookTypeId=tby.id;

左连接，查询t_book中所有信息，在t_bookType中查询不到用NULL代替
SELECT * FROM t_book LEFT JOIN t_bookType ON t_book.bookTypeId=t_bookType.id;

使用别名
SELECT tb.bookName,tb.author,tby.bookTypeName FROM t_book tb LEFT JOIN t_bookType tby ON tb.bookTypeId=tby.id;

右连接，查询t_bookType中所有信息，在t_book中查询不到用NULL代替
SELECT * FROM t_book RIGHT JOIN t_bookType ON t_book.bookTypeId=t_bookType.id;

使用别名
SELECT tb.bookName,tb.author,tby.bookTypeName FROM t_book tb RIGHT JOIN t_bookType tby ON tb.bookTypeId=tby.id;

多条件查询，查询大于70元的书的信息
SELECT tb.bookName,tb.author,tby.bookTypeName FROM t_book tb,t_bookType tby WHERE tb.bookTypeId=tby.id AND tb.price>70;