SQL NOT EXISTS和子查詢

Question

我有這2個表：

• Person（id, name, address, age）
• Knows（personA_id, personB_id）

，我想返回的Person的名字是比他們知道的Person大5歲以上。

我想這一點：

SELECT 
    P1.name 
FROM 
    Persons P1, Persons P2, Knows K1 
WHERE 
    P1.id = K1.personA_id 
    AND P2.id = K1.personB_id 
    AND NOT EXISTS (SELECT * 
        FROM Persons P3, Persons P4, Knows K2 
        WHERE P3.id = K2.personA_id 
         AND P4.id = K2.personB_id 
         AND (P3.age - P4.age) <= 5) 

但它不工作，我也不太清楚爲什麼。你能指點我正確的方向嗎？在此先感謝

Answer 1

如果你真的堅持存在，這可能做的伎倆：

SELECT p1.name AS the_older 
    , p2.name AS the_younger 
FROM Persons p1, Persons p2 
WHERE p1.age - p2.age > 5 -- They are more than 5 years older 
AND EXISTS (    -- than the one they know 
    SELECT * 
    FROM Knows Kx 
    WHERE Kx.personA_id = p1.id AND Kx.personB_id = p2.id 
    ); 

類似的東西可以用完成語法（年齡條件也可以移動到連接條件）：

SELECT p1.name AS the_older 
    , p2.name AS the_younger 
FROM Persons p1 
JOIN Persons p2 ON EXISTS (
    SELECT * FROM Knows Kx 
    WHERE Kx.personA_id = p1.id AND Kx.personB_id = p2.id 
    ) 
WHERE p1.age - p2.age > 5 
; 

---

UPDATE：後澄清的問題：

• 人物角色必須有一些朋友
• 所有的他們年齡超過5歲

---

SELECT p1.name 
FROM Persons p1 
WHERE EXISTS (-- must have friends 
    SELECT * FROM Knows Kx 
    WHERE Kx.personA_id = p1.id 
    ) 
AND NOT EXISTS (-- but no friends less than 5 years younger 
    SELECT * 
    FROM Knows Knx 
    JOIN Persons p2 ON Knx.personB_id = p2.id 
    WHERE Knx.personA_id = p1.id 
    AND p1.age - p2.age <= 5 
     ); 
    ); 

Answer 2

對於每個人，找到他們的年齡和他們認識的每個人的年齡。然後計算他們認識的人的最大年齡和篩選了這一點：

SELECT P1.name 
FROM Persons P1 JOIN 
    Knows K1 
    ON P1.id = K1.personA_id JOIN 
    Persons P2 
    ON P2.id = K1.personB_id 
GROUP BY P1.name, P1.age 
HAVING (p1.age - MAX(p2.age)) > 5; 

雖然你可以做到這一點使用exists，我覺得聚集是一個簡單的查詢和簡單的邏輯。

Answer 3

如果你只需要顯示關係，其中年齡相差> 5

SELECT P1.name 
FROM Persons P1 
INNER JOIN Knows K1 ON P1.id = K1.personA_id 
INNER JOIN Persons P2 ON P2.id = K1.personB_id 
WHERE (P1.age - P2.age) > 5 

，如果你只需要得到所有他們的關係至少有5歲的年齡差異的人則@Gordon Linoff答案是什麼您正在尋找

Answer 4

出發點是聯盟都知道表：

SELECT personA_id , 
      personB_id 
FROM  @k k 
UNION 
SELECT personB_id , 
      personA_id 
FROM  @k k 

因爲你會得到不正確的結果，如果你只是從一個側面驗證表知道了。

DECLARE @p TABLE 
    (
     id INT , 
     name NVARCHAR(MAX) , 
     age INT 
    ) 
DECLARE @k TABLE 
    (
     personA_id INT , 
     personB_id INT 
    ) 

INSERT INTO @p 
VALUES (1, 'a', 10), 
     (2, 'b', 14), 
     (3, 'c', 30), 
     (6, 'f', 35), 
     (7, 'g', 45) 


INSERT INTO @k 
VALUES (1, 2), 
     (1, 3), 
     (2, 3), 
     (7, 6) 


SELECT t.personA_id , 
     t.name 
FROM (SELECT personA_id , 
        name , 
        paage - pbage AS diff 
      FROM  (SELECT personA_id , 
           personB_id , 
           pa.age paage , 
           pb.age pbage , 
           pa.name 
         FROM  @k k 
           JOIN @p pa ON pa.id = k.personA_id 
           JOIN @p pb ON pb.id = k.personB_id 
         UNION 
         SELECT personB_id , 
           personA_id , 
           pb.age pbage , 
           pa.age paage , 
           pb.name 
         FROM  @k k 
           JOIN @p pa ON pa.id = k.personA_id 
           JOIN @p pb ON pb.id = k.personB_id 
        ) k 
     ) t 
GROUP BY t.personA_id , 
     t.name 
HAVING (MIN(diff) > 5) 

輸出：

personA_id name 
3   c 
7   g 

如果您將直接加入上表誰知，那麼你將得到：

SELECT t.personA_id , 
     t.name 
FROM (SELECT personA_id , 
        name , 
        paage - pbage AS diff 
      FROM  (SELECT personA_id , 
           personB_id , 
           pa.age paage , 
           pb.age pbage , 
           pa.name 
         FROM  @k k 
           JOIN @p pa ON pa.id = k.personA_id 
           JOIN @p pb ON pb.id = k.personB_id 
        ) k 
     ) t 
GROUP BY t.personA_id , 
     t.name 
HAVING (MIN(diff) > 5) 

輸出：

personA_id name 
7   g