如何在Postgres中選擇幾列而不按所有列分組

Question

我正在使用Postgres 8.4.2，並且嘗試進行查詢以選擇一些數據，但是按我選擇的這幾列分組時，我得到了錯誤的結果。

我嘗試不對所有這些列進行分組，但是我注意到，我應該對所有選定的列進行分組。

我的查詢如下所示：

 SELECT c.id AS category_id, c.parent_id, c.title AS category_title, count(ofrs.id) AS offers_count
   FROM categories c
   LEFT JOIN offers_to_categories otc ON c.id = otc.category_id
   LEFT JOIN offers ofrs ON otc.offer_id = ofrs.id
  WHERE ofrs.offer_type = 1 AND ofrs.status = 1
  GROUP BY c.id, c.title, c.parent_id;

我想選擇按offer_type = 1類別分類的商品。

如果不按幾列分組而僅按c.id分組，我怎么辦呢？

我嘗試了以下窗口函數，但結果是相同的-它向我顯示了比應有的結果更多的結果。

SELECT  ofr.id , c.id AS category_id, c.parent_id, c.title AS category_title,ofr.website_id ,
 count( ofr.id) 
 OVER (PARTITION BY  (ofr.id) order BY ofr.id)
 FROM offers AS ofr
 INNER JOIN offers_to_categories AS ofr_cat ON (ofr_cat.offer_id = ofr.id)
 INNER JOIN categories AS c ON (c.id = ofr_cat.category_id)
 WHERE (c.id = 3 or c.parent_id = 3) and ofr.website_id = 1 and ofr.status = 1

Answer 1

我找到了我的問題的答案，它是：

SELECT  distinct ON(ofr.id) ofr.id , c.id AS category_id, c.parent_id, c.title AS category_title,ofr.website_id ,
count( ofr.id) 
 OVER (PARTITION BY  (select distinct on(ofr.id) ofr.id from offers as id GROUP BY ofr.id) order BY ofr.id)
FROM offers AS ofr
INNER JOIN offers_to_categories AS ofr_cat ON (ofr_cat.offer_id = ofr.id)
INNER JOIN categories AS c ON (c.id = ofr_cat.category_id)
WHERE (c.id = 3 or c.parent_id = 3) and ofr.website_id = 1 and ofr.status = 1