Hive在两张桌子之间连接

Question

这就是问题a：我有一张暂存台：

key0    key1    timestamp   partition_key
5   5   2020-03-03 14:42:21.548 1
5   4   2020-03-03 14:40:11.871 1
4   3   2020-03-03 14:43:47.602 2

这个目标表：

key0    key1    timestamp   partition_key
5   4   2020-03-03 13:43:16.695 1
5   5   2020-03-03 13:45:24.793 1
5   2   2020-03-03 13:47:30.668 1
5   1   2020-03-03 13:48:30.669 1
4   3   2020-03-03 13:53:47.602 2
43  3   2020-03-03 14:00:14.016 2

我想得到这个输出：

key0    key1    timestamp   partition_key
5   5   2020-03-03 14:42:21.548 1
5   4   2020-03-03 14:40:11.871 1
5   2   2020-03-03 13:47:30.668 1
5   1   2020-03-03 13:48:30.669 1
4   3   2020-03-03 14:43:47.602 2
43  3   2020-03-03 14:00:14.016 2

在时间戳字段中，我想要key0、key1和partition_key时更新次数最多的记录。此外，我希望目标表中已经存在的记录，但在暂存表中不存在

我首先尝试了这个查询：

select 
t1.key0,
t1.key1,
t1.timestamp,
t2.partition_key
from staging_table t2 
left outer join target_table t1 on 
t1.key0=t2.key0 AND
t1.key1=t2.key1 AND
t1.timestamp=t2.timestamp; 

Answer 1

这看起来像是一个优先级查询——从暂存中获取所有内容，然后从目标中获取不匹配的行。我推荐union all:

select s.*
from staging s
union all
select t.*
from target t left join
staging s
on t.key0 = s.key0 and t.key1 = s.key1
where s.key0 is null;

这确实假设暂存具有最近的行——这在您的示例数据中是正确的。如果没有，我会把它说成：

select key0, key1, timestamp, partition_key
from (select st.*,
row_number() over (partition by key0, key1 order by timestamp desc) as seqnum
from ((select s.* from source s
) union all
(select t.* from target t
)
) st
) st
where seqnum = 1;

Answer 2

您需要FULL JOIN:

select COALESCE(t1.key0, T2.key0) AS key0, COALESCE(t1.key1, T2.KEY1) AS KEY1,
COALESCE(t1.timestamp, T2.timestamp) AS timestamp, 
COALESCE(t1.partition_key, t2.partition_key) AS partition_key
t2.partition_key
from staging_table t2 FULL JOIN 
target_table t1
on t1.key0 = t2.key0 AND t1.key1 = t2.key1 AND
t1.timestamp = t2.timestamp; 

Answer 3

我认为您只需要一个left join和coalesce():

select 
t.key0,
t.key1,
coalesce(s.timestamp, t.timestamp) timestamp,
t.partition_key
from target_table t 
left join  staging_table s 
on  s.key0 = t2.key0 
and s.key1 = t.key1 
and s.partition_key = t.partition_key

对于target_table中的每个记录，这将在staging_table中搜索具有相同(key0, key1, partition_key的记录(。如果这样的记录可用，我们使用它的timestamp来代替target_table中的timestamp。