獲取組後，「最新的」行通過在多個表

Question

我想最好喜歡的下方，只是stories.id組中列出的第一個查詢，但我得到了以下錯誤：

ERROR: column "u.first_name" must appear in the GROUP BY clause or be used in an aggregate function LINE 1: SELECT "s".*, "u"."first_name", "u"."last_name", ("i"."filen...

第二個查詢作品但不會按stories.id分組，並生成錯誤的結果。是否可以從多個表中進行選擇而不是全部進行分組？

表panels也有一列updated_at。我想根據panels.updated_at得到每個故事最新的file。

SELECT 
     "s".*, 
     "u"."first_name", 
     "u"."last_name", 
     ("i"."filename" || '.' || "i"."extension") AS "file" 
    FROM 
     "stories" "s" 
    LEFT JOIN "panels" "p" ON("p"."story_id" = "s"."id") 
    LEFT JOIN "users" "u" ON("s"."user_id" = "u"."uid") 
    LEFT JOIN "images" "i" ON ("p"."image_id" = "i"."id") 
    WHERE 
     "s"."complete" = false AND 
     "s"."created_by" = 205700489 
    GROUP BY 
     "s"."id", 
    ORDER BY 
     "s"."created_at" DESC 

---

SELECT 
     "s".*, 
     "u"."first_name", 
     "u"."last_name", 
     ("i"."filename" || '.' || "i"."extension") AS "file" 
    FROM 
     "stories" "s" 
    LEFT JOIN "panels" "p" ON("p"."story_id" = "s"."id") 
    LEFT JOIN "users" "u" ON("s"."user_id" = "u"."uid") 
    LEFT JOIN "images" "i" ON ("p"."image_id" = "i"."id") 
    WHERE 
     "s"."complete" = false AND 
     "s"."created_by" = 205700489 
    GROUP BY 
     "s"."id", 
     "u"."first_name", 
     "u"."last_name", "i"."filename", 
     "i"."extension" 
    ORDER BY 
     "s"."created_at" DESC 

Answer 1

問題澄清後更新：

SELECT DISTINCT ON (s.created_at, s.id) 
     s.* 
     ,u.first_name 
     ,u.last_name 
     ,concat_ws('.', i.filename, i.extension) AS file 
FROM stories s 
LEFT JOIN users u ON u.uid = s.user_id 
LEFT JOIN panels p ON p.story_id = s.id 
LEFT JOIN images i ON i.id = p.image_id 
WHERE s.complete = false 
AND s.created_by = 205700489 
ORDER BY s.created_at DESC, s.id, p.updated_at DESC; 

Grouping by primary key需要PostgreSQL 9.1。
我使用concat_ws()，因爲我不知道哪些列可能是NULL。如果i.filename和i.extension都定義爲NOT NULL，則可以簡化。

額外的ORDER BY項目p.updated_at DESC的影響是每個故事將挑選「最新」file。查詢技術在這個相關的問題下全部解釋：
Select first row in each GROUP BY group?

Answer 2

您可以編寫類似：

SELECT 
     "s".*, 
     (SELECT "u"."first_name" 
     FROM "users" "u" 
     WHERE "s"."user_id" = "u"."uid" 
     LIMIT 1) , 
     (SELECT "u"."last_name" 
     FROM "users" "u" 
     WHERE "s"."user_id" = "u"."uid" 
     LIMIT 1), 
     (SELECT "i"."filename" || '.' || "i"."extension" 
     FROM "panels" "p" 
     JOIN "images" "i" ON ("p"."image_id" = "i"."id") 
     WHERE "p"."story_id" = "s"."id" 
     LIMIT 1) AS "file" 
    FROM 
     "stories" "s" 
    WHERE 
     "s"."complete" = false AND 
     "s"."created_by" = 205700489 
    ORDER BY 
     "s"."created_at" DESC 

它將從"users"和"panels" JOIN "images"只得到1創紀錄的紀錄"stories"。

添加ORDER BY，額外WHERE或一些聚集，讓你從"users"和"panels" JOIN "images"需要

UPD此外，您還可以使用類似這樣的內容：

SELECT * 
FROM (
SELECT DISTINCT ON ("s"."id") 
    "s".*, 
    "u"."first_name", 
    "u"."last_name", 
    ("i"."filename" || '.' || "i"."extension") AS "file" 
FROM 
    "stories" "s" 
LEFT JOIN "panels" "p" ON("p"."story_id" = "s"."id") 
LEFT JOIN "users" "u" ON("s"."user_id" = "u"."uid") 
LEFT JOIN "images" "i" ON ("p"."image_id" = "i"."id") 
WHERE 
    "s"."complete" = false AND 
    "s"."created_by" = 205700489 
ORDER BY 
    "s"."id" 
) t ORDER BY "t"."created_at" DESC 

這將只留下一排，每不同"s"."id"