hive sql须要注意的地方(持续更新)

基于hive-1.2.1版本

1.join 与 where的顺序

t_user                                                   job

userId    userName                           userId    jobId

1            user1                                    4            3

2            user2                                    5            3

select * from t_user t1 left join job t2 on t1.userId=t2.userId  where t2.jobId=3  (没有结果)

select * from t_user t1 left join (select * from job where jobId=3 ) t2 on t1.userId=t2.userId （两条）

2.sum()时注意null值

hive> select * from tbl3;
OK
1    1
2    2
NULL    3
3    4

hive> select sum(num1),sum(num2+num1) from tbl3;

OK
6    13

hive> select sum(num1),sum(num2+nvl(num1,0)) from tbl3;

OK 6    16