sql - 如何在 PostgreSQL 中每组获取一行？

Question

我有以下数据:

customerid addressid
939          936
939          35485
1915         2224
1915         34236
6005         7012
6005         27914

由这个查询给出:

select customerid ,addressid
from addresses
where .....

我希望查询只为每位客户返回一个地址，我不在乎是哪个地址。所以期望的输出可以是:

addressid
936
2224
7012

或

addressid
936
34236
7012

等..

我尝试过:

select DISTINCT customerid ,addressid
from addresses
where .....

但它什么也没做...我想做 GROUP BY customerid 但后来我丢失了 addressid。我该怎么做？

Answer 1

如果您不关心它是哪个 addressid，这是一个简单的 group by:

select customerid, max(addressid) as addressid
from addresses
group by customerid