Sql Postgres：基于列中的多个值获取聚合查询

我有以下数据库表：

id, owner_id, partner_id, level
1, 121, 234, gold
2, 121, 342, silver
3, 121, 423, silver
4, 233, 333, silver
5, 233, 434, gold

我试图以以下格式获得结果：

owner_id, number_of_partners, total_gold, total_silver, total_bronze

我不确定这是否可行，到目前为止，我从基本的groupby查询开始，从那里可以得到每个所有者的合作伙伴总数

SELECT owner_id, count(partner_id) FROM owner_partner GROUP BY owner_id

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如何扩展此功能以获得结果？

只需使用条件聚合：

SELECT owner_id, count(partner_id),
       sum(case when level = 'gold' then 1 else 0 end) as gold,
       sum(case when level = 'silver' then 1 else 0 end) as silver,
       sum(case when level = 'bronze' then 1 else 0 end) as bronze
FROM owner_partner
GROUP BY owner_id;

我建议缩短语法（与

CASE

语句的性能大致相同）：

SELECT owner_id
     , count(*) AS total
     , count(level = 'gold' OR NULL) AS gold
     , count(level = 'silver' OR NULL) AS silver
     , count(level = 'bronze' OR NULL) AS bronze
FROM   tbl
GROUP  BY 1;