[英]Max of each subgroup in a group
So I have a table with following data : 所以我有一个表,其中包含以下数据:
X------------------Y
customer1------A
customer1------A
customer1------B
customer2------B
customer2------B
customer2------B
customer2------C
customer2------C
customer2------C
customer2------C
customer2------C
So I need to find what max(Y) does each customer have. 因此,我需要找到每个客户拥有的max(Y)。 So customer1 must have B and customer2 must have C (I'm using postgresql)
因此,customer1必须具有B,customer2必须具有C(我正在使用PostgreSQL)
You want the "mode" in statistics. 您需要统计中的“模式”。 Here is one method to get exactly one value per x (ignoring duplicates):
这是一种获取每x精确值一个的方法(忽略重复项):
select distinct on (x) x, y
from (select x, y, count(*) as cnt
from t
group by x, y
) xy
order by x, cnt desc;
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