inner            left               right                   full   
 
 
 
 在sql中的join                                                                                      union all
 
 select * from test_hadoop_pig t1 join test_hadoop_key t2 on t1.prov_id=t2.key
 
 在hadoop pig 的join    
 
joinName = join load2_output by ( id ) FULL ,load1 by ( id ) ;