PostgreSQL 不同，分组依据，合二为一？

Question

我在使用 PostgreSQL 查询时遇到了一些问题

我想要的是一个“活动”列表，按距离排序，并且在距某个位置 [in_lat, in_lng, in_radius] 的最小距离内 现在，我正在检索距离（使用 distance_in_km(...) ）两次。一次用于订购，一次用于检查广告系列是否在我的首选范围内。

此外，一个活动可能有多个“活动接收者”条目（接收类型 [EMAIL、WEBSITE 等...]）

我只想检索一次广告系列。因此 DISTINCT ON。

所以问题是，我怎样才能让“WHERE distance

非常感谢任何帮助！！！

    SELECT DISTINCT ON (c.campaign_uuid, distance)
            c.campaign_uuid,
            prl.lat,
            prl.long,
            distance_in_km(prl.lat, prl.long, in_lat, in_lng) AS distance                
        FROM 
            usercampaignrelations AS ucr
        LEFT JOIN
            campaignreceivers AS cr
        ON
            ucr.usercampaign_uuid = cr.usercampaign_uuid
        LEFT JOIN
            campaigntargetgrouprelations AS ctg
        ON
            cr.campaigntargetgroup_uuid = ctg.campaigntargetgroup_uuid
        LEFT JOIN
            campaigns AS c
        ON
            ucr.campaign_uuid = c.campaign_uuid
        LEFT JOIN
            companycampaignrelations AS cc
        ON
            c.campaign_uuid = cc.campaign_uuid
        LEFT JOIN
            pointradiuslocations AS prl
        ON
            c.location_uuid = prl.location_uuid
        WHERE 
            ucr.user_uuid = in_user_uuid
        AND
            (cr.status = 'SENT' OR cr.status = 'RETRIEVED')
        AND
            distance_in_km(prl.lat, prl.long, in_latitude, in_longtitude) < in_radius
        ORDER BY
            distance
        LIMIT 
            in_limit

Answer 1

AFAIK，distance_in_km() 只会被调用一次（每行），只要你使用相同的参数，因此 WHERE 和 ORDER BY 不会再次评估它。