Hive&SqlServerql：inner join on條件中如果兩邊都是空值的情況下，關聯結果中會把數據給過濾掉。

今天遇到的一個大坑，話不多少，看sql和下邊的查詢結果：

--問題：恰好把buildingid is null的記錄給過濾掉
create table tommyduan_gridcell_group_all_test(gridid nvarchar(32),buildingid nvarchar(32),floor nvarchar(32));
insert into tommyduan_gridcell_group_all_test(gridid,buildingid,floor)values('g1',null,1);
insert into tommyduan_gridcell_group_all_test(gridid,buildingid,floor)values('g2','b1',1);
insert into tommyduan_gridcell_group_all_test(gridid,buildingid,floor)values('g2','b2',1);
insert into tommyduan_gridcell_group_all_test(gridid,buildingid,floor)values('g3','b2',1);
insert into tommyduan_gridcell_group_all_test(gridid,buildingid,floor)values('g3','b2',2);
insert into tommyduan_gridcell_group_all_test(gridid,buildingid,floor)values('g3','b2',4);


create table tommyduan_fingerlib(gridid nvarchar(32),buildingid nvarchar(32),floor nvarchar(32));
insert into tommyduan_fingerlib(gridid,buildingid,floor)values('g1',null,1);
insert into tommyduan_fingerlib(gridid,buildingid,floor)values('g2','b1',1);
insert into tommyduan_fingerlib(gridid,buildingid,floor)values('g2','b2',1);
insert into tommyduan_fingerlib(gridid,buildingid,floor)values('g3','b2',1);
insert into tommyduan_fingerlib(gridid,buildingid,floor)values('g3','b2',2);
insert into tommyduan_fingerlib(gridid,buildingid,floor)values('g3','b2',4);


select * from tommyduan_gridcell_group_all_test t10 
inner join tommyduan_fingerlib t11 
on t10.gridid=t11.gridid and t10.buildingid=t11.buildingid and t10.floor=t11.floor

查詢結果：

解決方案：

select * from 
(
select gridid,buildingid,floor,gridid+(case when buildingid is null then 'd_null' else buildingid end)+floor as tkey 
from tommyduan_gridcell_group_all_test
) t10 
inner join 
(
select gridid,buildingid,floor,gridid+(case when buildingid is null then 'd_null' else buildingid end)+floor as tkey 
from tommyduan_fingerlib
)  t11 
on t10.tkey=t11.tkey

查詢結果：

left outer join時的查詢結果是：

select * from tommyduan_gridcell_group_all_test t10 
left outer join tommyduan_fingerlib t11 
on t10.gridid=t11.gridid and t10.buildingid=t11.buildingid and t10.floor=t11.floor