[英]SQL (Hive) group-by using nulls as wildcard
I have a table like this:我有一张这样的桌子:
group val1 val2 val3
group1 5 . .
group1 . 2 1
group1 . . 3
group2 1 4 .
group2 . . 8
group2 2 . 7
I need to count the occurrences of all possible combinations for each group in Hive, using null values (.) as a wildcard.我需要使用 null 值 (.) 作为通配符,计算 Hive 中每个组的所有可能组合的出现次数。 This would give me results like this:
这会给我这样的结果:
group val1 val2 val3 cnt
group1 5 2 1 2
group1 5 2 3 2
group2 1 4 8 2
group2 2 4 8 1
group2 2 4 7 1
I know I can do this by selecting all distinct group-val1 pairs, full joining this with all distinct group-val2 pairs, and full joining this with all distinct group-val3 pairs.我知道我可以通过选择所有不同的 group-val1 对,将其与所有不同的 group-val2 对完全连接,并将其与所有不同的 group-val3 对完全连接来做到这一点。 This gives me all possible combinations for each group, which I can then inner join with my table, counting cases where a row of my original data is a subset of a combination.
这为我提供了每个组的所有可能组合,然后我可以将它们与我的表进行内部连接,计算我的原始数据行是组合子集的情况。
Something like this:像这样的东西:
create table my_results as
with combos as (
select *
from (select distinct group, val1 from data) A
full join (select distinct group, val2 from data) B
on A.group = B.group
full join (select distinct group, val3 from data) C
on A.group = C.group
)
select A.group, A.val1, A.val2, A.val3, count(*)
from combos A
inner join data B
on A.group = B.group
and (A.val1 = B.val1 OR B.val1 is null)
and (A.val2 = B.val2 OR B.val2 is null)
and (A.val3 = B.val3 OR B.val3 is null)
group by A.group, A.val1, A.val2, A.val3
But, My dataset is very large (100s of millions of rows).但是,我的数据集非常大(数百万行)。 and the number of all possible combinations I can expect is also very large (10s of thousands).
并且我可以预期的所有可能组合的数量也非常大(成千上万)。 Such a join is just too big.
这样的连接太大了。
Is there another way?还有其他方法吗? I wondered if I could use regular expressions, but I don't know where to start.
我想知道是否可以使用正则表达式,但我不知道从哪里开始。
In your sample data, only the third column has multiple values.在您的示例数据中,只有第三列有多个值。 So, you could just fill in the one value for the two other columns:
因此,您可以只为另外两列填写一个值:
select group,
max(max(col1)) over (partition by group) as col1,
max(max(col2)) over (partition by group) as col2,
col3,
count(*)
from data
group by group;
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