如何將這兩個SQL查詢合並為一個？

Question

顯示請求多於報價的城市。

我進行了這兩個查詢，以顯示每個城市的消費者有多少個請求，然后向每個城市的有報價的供應商提出一個請求。 是的，這是實驗室的一部分，每個輸出都給了我，但是我已經堅持了2個小時，並且嘗試了所有我能想到的東西，這也是最后一個問題。

SELECT COUNT(c.Con_ID) 'Requests', city
FROM tb_requests r, Tb_Consumer c, Tb_Product p
WHERE r.Con_ID = c.Con_ID
  AND r.Prod_ID = p.Prod_ID
  ANd p.Name = 'computer'
  group by city

SELECT COUNT(s.supp_id) 'Offers', city
FROM Tb_offers o, Tb_supplier s, Tb_Product p
WHERE o.supp_ID = s.supp_ID
  AND o.Prod_ID = p.Prod_ID
  ANd p.Name = 'computer'
  GROUP By city

輸出是這樣的：

Number      city
----------- ------------------------------
2           New York
4           Wausau

(2 row(s) affected)

Number      city
----------- ------------------------------
2           Chicago
1           London
4           Madison
2           Stevens Point
3           Wausau

(5 row(s) affected)

正確的輸出應該是這樣（它們在一起）：

City                           Computer Offers Computer Requests
------------------------------ --------------- -----------------
Wausau                         3               4

(1 row(s) affected)

非常感謝！

Answer 1

當您詢問SQL問題時，請添加您的DBMS（例如MySQL，SQL Server，PostgreSQL等）

這不僅困擾着您，而且對於SQL，語法可能會因數據庫的不同而發生很大變化。

---

說完之后，我將使用ANSI SQL（應該在每個體面的DB上都可以使用）：

SELECT t1.city, Offers, Requests
FROM (
    SELECT COUNT(c.Con_ID) Requests, city
    FROM tb_requests r, Tb_Consumer c, Tb_Product p
    WHERE r.Con_ID = c.Con_ID
    AND r.Prod_ID = p.Prod_ID
    ANd p.Name = 'computer'
    group by city
    ) t1
INNER JOIN (
    SELECT COUNT(s.supp_id) Offers, city
    FROM Tb_offers o, Tb_supplier s, Tb_Product p
    WHERE o.supp_ID = s.supp_ID
    AND o.Prod_ID = p.Prod_ID
    ANd p.Name = 'computer'
    GROUP By city
    ) t2
    ON t1.city = t2.city
WHERE Requests > Offers

如果您想要更清潔的東西，應該做的完全一樣：

SELECT city, COUNT(s.supp_id) Offers, COUNT(c.Con_ID) Requests
FROM Tb_Product p
    LEFT JOIN Tb_offers o ON p.Prod_ID = o.Prod_ID
        LEFT JOIN Tb_supplier s ON o.supp_ID = s.supp_ID
    LEFT JOIN tb_requests r ON p.Prod_ID = r.Prod_ID
        LEFT JOIN Tb_Consumer c ON r.Con_ID = c.Con_ID
WHERE p.Name = 'computer'
GROUP BY city
HAVING COUNT(c.Con_ID) > COUNT(s.supp_id)