将 SELECT 子查询与别名和 FROM 一起使用

Question

我正在尝试对别名子查询进行计数和来自，但无法弄清楚如何添加过滤部分：

SELECT  webpages.*, (select count(*) 
                     from webpage_opportunities 
                     where webpage_opportunities.webpage_id = webpages.id) as test_count 
FROM "webpages" 
WHERE (webpages.clicks IS NOT NULL) AND "webpages"."website_id" = 144 AND test_count = 0
GROUP BY webpages.id ORDER BY "webpages"."clicks" DESC LIMIT 50 OFFSET 0

当我删除AND test_count = 0 时，查询结果中会显示test_count 列，但是一旦添加它，查询就会失败。我还需要确保子查询连接到网页表，如上面 thje join 中所述。

Answer 1

SELECT  w.*, COUNT(wo.id) -- but will be 0 because the HAVING
FROM webpages w
LEFT JOIN webpage_opportunities wo
  ON w.id = wo.webpage_id
WHERE (w.clicks IS NOT NULL) 
  AND w."website_id" = 144
GROUP BY w.id 
HAVING COUNT(wo.id) = 0
ORDER BY w."clicks" DESC 
       , COUNT(wo.id) -- optional
LIMIT 50 OFFSET 0