mysql 内连接、左连接、右连接

DROP TABLE IF EXISTS t_demo_product;
CREATE TABLE IF NOT EXISTS t_demo_product(
    proid int(20),
    proname varchar(20),
    price int(10),
    PRIMARY KEY(proid)
)ENGINE=InnoDB  DEFAULT CHARSET=gbk;

DROP TABLE IF EXISTS t_demo_operation;
CREATE TABLE IF NOT EXISTS t_demo_operation(
    opid  int(10),
    proid int(20),
    opcount int(10),
    PRIMARY KEY(opid)
)ENGINE=InnoDB  DEFAULT CHARSET=gbk;


insert into t_demo_product(proid, proname, price) values
(1,‘产品A‘,‘10‘)
,(2,‘产品B‘,‘11‘)
,(3,‘产品C‘,‘12‘)
,(4,‘产品D‘,‘13‘)
,(5,‘产品E‘,‘14‘);

insert into t_demo_operation(opid, proid, opcount) values
(1,1,2)
,(2,3,6)
,(3,3,1)
,(4,4,3)
,(5,7,3);