如何计算Postgresql忽略一对多连接的结果量

我有一个非常大的查询，有多个连接，我还需要使用相同的连接进行查询，但是没有

limit/offset

功能，只是为了获取分页的行总数

我将把这里的查询简化为单连接，并省略所有where子句

我有5个提议，每个提议有2个活动

主查询：

SELECT o.id                       AS "id",
       o.display_name             AS "displayName",
       o.offer_hidden             AS "offerHidden",
       o.offer_type               AS "offerType",
       array_to_json(o.countries) AS "countries",
       string_agg(distinct concat(COALESCE(e.event_id::text, ''), ',, ', COALESCE(e.event_tag::text, ''), ',, ',
                                  COALESCE(e.payout::text, '')), ';;') AS "events"
FROM offer o
                  INNER JOIN (SELECT e.event_id, e.event_tag, e.payout, e.offer_id FROM event e ORDER BY e.offer_id ASC) e
                                                                     ON e.offer_id = o.id
GROUP BY o.id

SELECT count(1) AS count
FROM offer o
         INNER JOIN (SELECT e.event_id, e.event_tag, e.payout, e.offer_id FROM event e ORDER BY e.offer_id ASC) e
                    ON e.offer_id = o.id

正如您在这里看到的，我正在为活动制作

concat

和

string\u add

，以获得每个报价的单个记录

计数查询：

SELECT o.id                       AS "id",
       o.display_name             AS "displayName",
       o.offer_hidden             AS "offerHidden",
       o.offer_type               AS "offerType",
       array_to_json(o.countries) AS "countries",
       string_agg(distinct concat(COALESCE(e.event_id::text, ''), ',, ', COALESCE(e.event_tag::text, ''), ',, ',
                                  COALESCE(e.payout::text, '')), ';;') AS "events"
FROM offer o
                  INNER JOIN (SELECT e.event_id, e.event_tag, e.payout, e.offer_id FROM event e ORDER BY e.offer_id ASC) e
                                                                     ON e.offer_id = o.id
GROUP BY o.id

SELECT count(1) AS count
FROM offer o
         INNER JOIN (SELECT e.event_id, e.event_tag, e.payout, e.offer_id FROM event e ORDER BY e.offer_id ASC) e
                    ON e.offer_id = o.id

在这里，我试图使查询尽可能轻量级，忽略所有选择并使用唯一计数，但我得到计数10，因为每个提供有2个事件（5*2=10）

问题：是否可以仅按主表进行计数，但仍使用联接中的数据进行筛选/排序

更新：我知道我可以将相同的

concat

和

string\u agg

添加到计数查询中，但此查询应该是轻量级的，因为它将查询具有

限制/偏移量的所有记录

更新：看来我找到了一个可能的解决方案，使用了
distinct

SELECT count(distinct o.id) AS count
FROM offer o
         INNER JOIN (SELECT e.event_id, e.event_tag, e.payout, e.offer_id FROM event e ORDER BY e.offer_id ASC) e
                    ON e.offer_id = o.id

但不确定这样做的最佳方式是什么
您应该使用半连接：

SELECT count(*) AS count
FROM offer o
WHERE EXISTS (SELECT 1 FROM event e WHERE e.offer_id = o.id);

这将比使用
DISTINCT
更快