單個條件給出與WHERE條件相同的輸出

Question

我試圖撰寫一個關於的查詢data.stackexchange.com這會給我這個問題的答案是什麼百分比的用戶誰寫了超過1000時間和誰擁有某一類的徽章。

問題：如果我寫AND ViewCount > 1000我得到了相同的結果WHERE ViewCount > 1000 我不明白爲什麼會發生

與該查詢：

SELECT 
TOP 1000 
Class, (Count(Badges.UserId)* 100/(SELECT COUNT(*) From Badges)) AS Percentage 
FROM Badges 
WHERE Badges.UserId IN (SELECT Posts.OwnerUserId FROM Posts 
INNER JOIN 
Badges ON Posts.OwnerUserId = Badges.UserId 
WHERE ViewCount > 1000) 
GROUP BY Class 
ORDER BY Class 

查詢與AND：

SELECT 
TOP 1000 
Class, (Count(Badges.UserId)* 100/(SELECT COUNT(*) From Badges)) AS Percentage 
FROM Badges 
WHERE Badges.UserId IN (SELECT Posts.OwnerUserId FROM Posts 
INNER JOIN 
Badges ON Posts.OwnerUserId = Badges.UserId 
AND ViewCount > 1000) 
GROUP BY Class 
ORDER BY Class 

輸出（由於某種原因，它在b中是相同的OTH例）：

1類 - 2％

2類 - 15％

3類 - 45％

Answer 1

您正在使用AND到兩個表達式連接在的ON條件JOIN。專注於內部查詢：

SELECT Posts.OwnerUserId FROM Posts 
INNER JOIN Badges ON Posts.OwnerUserId = Badges.UserId 
WHERE ViewCount > 1000 

對戰：

SELECT Posts.OwnerUserId FROM Posts 
INNER JOIN Badges 
ON (
    Posts.OwnerUserId = Badges.UserId 
    AND ViewCount > 1000 
) 

這兩個查詢是邏輯上等同。

Answer 2

請與此檢查，如果你是混淆了作爲下同情況： 在SQL Server

CREATE TABLE #a(catId INT, catName VARCHAR(50)) 
CREATE TABLE #b(productId INT, catId INT) 

INSERT INTO #a VALUES 
(1, 'Test1'), 
(2, 'Test2'), 
(3, 'Test3'), 
(4, 'Test4') 

INSERT INTO #b VALUES 
(5, 1), 
(6, 2), 
(7, 3), 
(8, 1) 

--Return data what exists in both tables 
SELECT a.*, b.productId 
FROM #a a 
INNER JOIN #b b ON b.catId = a.catId 
AND b.catId < 3 

--Same as above 
SELECT a.*, b.productId 
FROM #a a 
INNER JOIN #b b ON b.catId = a.catId 
WHERE b.catId < 3 

--Same as above 
SELECT a.*, b.productId 
FROM #a a 
LEFT JOIN #b b ON b.catId = a.catId 
WHERE b.catId < 3 

--Return all exists in first table though not exist in second table 
SELECT a.*, b.productId 
FROM #a a 
LEFT JOIN #b b ON b.catId = a.catId 
AND b.catId < 3