[英]Sort items based on results that may or may not be in join table in rails
[英]mysql query to sort some results but join data may or not be present
SELECT PLD_LINK.ID, PLD_LINK.TITLE, PLD_LINK.URL, PLD_CATEGORY.TITLE, TLL_SORT_STATUS.status, PLD_LINK_COMMENT.DATE_ADDED
FROM PLD_LINK, PLD_CATEGORY, TLL_SORT_STATUS, PLD_LINK_COMMENT
WHERE PLD_LINK.CATEGORY_ID = PLD_CATEGORY.ID
AND PLD_LINK.ID = TLL_SORT_STATUS.link_id
AND PLD_LINK.PAGERANK BETWEEN -1 AND 2
AND PLD_LINK.CATEGORY_ID IN (1291,2113,2664)
ORDER BY COUNT(PLD_LINK.ID = PLD_LINK_COMMENT.LINK_ID) ASC
這是我的查詢。 我想獲得所有在ORDER BY之前匹配的結果。 現在,來自PLD_LINK.ID的某些ID可能在表PLD_LINK_COMMENT中,但有些可能不在。 因此,當mysql達到ORDER BY時,我想根據以下條件按升序對結果進行排序:不在PLD_LINK_COMMENT中的ID應該是第一個,然后是基於每個ID的評論數的ID。 。 (ID不能有1、2 ...條注釋。)
您需要在三個主表和PLD_LINK_COMMENT之間進行外部聯接。
外部聯接意味着PLD_LINK_COMMENT.LINK_ID為空,這意味着COUNT將為PLD_LINK.ID返回0,且沒有匹配的鏈接注釋,而其他注釋的數目則適當。
您需要按未聚合的列進行分組……但是這表明M.Date_Added可能不是您要分組的; 並且評論中的問題/答案表明我們需要最新的評論日期,或者一些荒謬的早期數據,例如“ 0001-01-01”(SQL中最早的有效日期)或“ 0000-00-00”(偽-MySQL使用的日期)。
因此:
SELECT K.ID, K.Title, K.URL, C.Title, S.Status,
MAX(NVL(M.Date_Added, DATE '0001-01-01')) AS MostRecentComment
FROM Pld_Link AS K JOIN Pld_Category AS C ON K.Category_ID = C.ID
JOIN Tll_Sort_Status AS C ON K.ID = S.Link_ID
OUTER JOIN Pld_Link_Comment AS M ON K.ID = M.Link_ID
WHERE K.PageRank BETWEEN -1 AND 2
AND K.Category_ID IN (1291,2113,2664)
GROUP BY K.ID, K.Title, K.URL, C.Title, S.Status
ORDER BY COUNT(M.Link_ID) ASC
您還需要DBMS(您所說的MySQL)來允許您按SELECT列表中未列出的列進行排序。
在MacOS X 10.6.2上使用IBM Informix Dynamic Server 11.50進行了測試。 我使用DATE('0001-01-01')
是因為IDS具有一個稱為DATE的函數,該函數需要括號,而我使用了“ 0001-01-01”是因為IDS無法將'0000-00-00'識別為有效日期。
SELECT K.ID, K.Title, K.URL, C.Title, S.STATUS,
MAX(NVL(M.Date_Added, DATE('0001-01-01'))) AS MostRecentComment,
FROM PLD_Link AS K JOIN PLD_Category AS C ON K.Category_ID = C.ID
JOIN Tll_Sort_Status AS S ON K.ID = S.Link_ID
LEFT OUTER JOIN PLD_Link_Comment AS M ON K.ID = M.Link_ID
WHERE K.PageRank BETWEEN -1 AND 2
AND K.Category_ID IN (1291,2113,2664)
GROUP BY K.ID, K.Title, K.URL, C.Title, S.STATUS
ORDER BY COUNT(M.Link_ID)
結果:
id title url title status mostrecent
4 #4: This should show example.com/?id=4;c=2113 Cat 2113 0 0001-01-01
3 #3: This should show example.com/?id=3;c=1291 Cat 1291 -1 2010-03-10
7 #7: This should show example.com/?id=7;c=2664 Cat 2664 3 2010-07-11
5 #5: This should show example.com/?id=5;c=2113 Cat 2113 1 2010-05-17
2 #2: This should show example.com/?id=2;c=1291 Cat 1291 -2 2010-02-13
或者,選擇評論計數,以顯示數據以正確的順序顯示。
SELECT K.ID, K.Title, K.URL, C.Title, S.STATUS,
MAX(NVL(M.Date_Added, DATE('0001-01-01'))) AS MostRecentComment,
COUNT(M.Link_ID) AS CommentCount
FROM PLD_Link AS K JOIN PLD_Category AS C ON K.Category_ID = C.ID
JOIN Tll_Sort_Status AS S ON K.ID = S.Link_ID
LEFT OUTER JOIN PLD_Link_Comment AS M ON K.ID = M.Link_ID
WHERE K.PageRank BETWEEN -1 AND 2
AND K.Category_ID IN (1291,2113,2664)
GROUP BY K.ID, K.Title, K.URL, C.Title, S.STATUS
ORDER BY CommentCount ASC;
結果集:
id title url title status recent count
4 #4: This should show example.com/?id=4;c=2113 Cat 2113 0 0001-01-01 0
3 #3: This should show example.com/?id=3;c=1291 Cat 1291 -1 2010-03-10 1
7 #7: This should show example.com/?id=7;c=2664 Cat 2664 3 2010-07-11 1
5 #5: This should show example.com/?id=5;c=2113 Cat 2113 1 2010-05-17 2
2 #2: This should show example.com/?id=2;c=1291 Cat 1291 -2 2010-02-13 3
CREATE TABLE PLD_Category
(
ID SERIAL NOT NULL PRIMARY KEY,
Title VARCHAR(32) NOT NULL
);
INSERT INTO PLD_Category VALUES(3961, 'Cat 3961');
INSERT INTO PLD_Category VALUES(1291, 'Cat 1291');
INSERT INTO PLD_Category VALUES(2113, 'Cat 2113');
INSERT INTO PLD_Category VALUES(2664, 'Cat 2664');
CREATE TABLE PLD_Link
(
ID SERIAL NOT NULL PRIMARY KEY,
Category_ID INTEGER NOT NULL REFERENCES PLD_Category,
Title VARCHAR(32) NOT NULL,
PageRank INTEGER NOT NULL,
URL VARCHAR(64) NOT NULL
);
INSERT INTO PLD_Link
VALUES(1, 3961, '#1: This should not', 0, 'example.com/?id=1;c=3961');
INSERT INTO PLD_Link
VALUES(2, 1291, '#2: This should show', 0, 'example.com/?id=2;c=1291');
INSERT INTO PLD_Link
VALUES(3, 1291, '#3: This should show', 0, 'example.com/?id=3;c=1291');
INSERT INTO PLD_Link
VALUES(4, 2113, '#4: This should show', 0, 'example.com/?id=4;c=2113');
INSERT INTO PLD_Link
VALUES(5, 2113, '#5: This should show', 0, 'example.com/?id=5;c=2113');
INSERT INTO PLD_Link
VALUES(6, 3961, '#6: This should not', 0, 'example.com/?id=6;c=3961');
INSERT INTO PLD_Link
VALUES(7, 2664, '#7: This should show', 0, 'example.com/?id=7;c=2664');
INSERT INTO PLD_Link
VALUES(8, 2664, '#8: This should show', 0, 'example.com/?id=8;c=2664');
CREATE TABLE TLL_Sort_Status
(
STATUS INTEGER NOT NULL,
Link_ID INTEGER NOT NULL REFERENCES PLD_Link
);
INSERT INTO TLL_Sort_Status VALUES(-3, 1);
INSERT INTO TLL_Sort_Status VALUES(-2, 2);
INSERT INTO TLL_Sort_Status VALUES(-1, 3);
INSERT INTO TLL_Sort_Status VALUES( 0, 4);
INSERT INTO TLL_Sort_Status VALUES(+1, 5);
INSERT INTO TLL_Sort_Status VALUES(+2, 6);
INSERT INTO TLL_Sort_Status VALUES(+3, 7);
INSERT INTO TLL_Sort_Status VALUES(+4, 1);
CREATE TABLE PLD_Link_Comment
(
Link_ID INTEGER NOT NULL REFERENCES PLD_Link,
Date_Added DATE NOT NULL,
COMMENT VARCHAR(64) NOT NULL
);
INSERT INTO PLD_Link_Comment VALUES(1, DATE('2010-01-11'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(2, DATE('2010-02-11'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(2, DATE('2010-02-12'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(2, DATE('2010-02-13'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(3, DATE('2010-03-10'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(5, DATE('2010-05-15'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(5, DATE('2010-05-17'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(6, DATE('2010-06-10'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(6, DATE('2010-06-12'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(6, DATE('2010-06-14'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(6, DATE('2010-06-19'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(7, DATE('2010-07-11'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(8, DATE('2010-08-12'), 'Vacuous comment');
INSERT INTO PLD_Link_Comment VALUES(8, DATE('2010-08-13'), 'Vacuous comment');
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