9、select * from table1 left join table2 on table1.id=table2.id-------------结果-------------idnameidscore------------------------------1lee1902zhang21004wangNULLNULL-----------------
10、-------------select * from table1 join table2 on table1.id=table2.id-------------结果-------------idnameidscore------------------------------1lee1902zhang2100select * from table1 full join table2 on table1.id=table2.id-------------结果-------------idnameidscore------------------------------1lee1902z
11、hang21004wangNULLNULLNULLNULL370select * from table1 right join table2 on table1.id=table2.id-------------结果-------------idnameidscore------------------------------1lee1902zhang2100NULLNULL370------------------------------连接简介MapReduce连接策略连接连接是关系运算,可以用于合并关系。在数据库中,一般是表连接操作;在MapReduce中,连接可以用于合并两个或