Sql 如何从表中选择重复项

考虑这个名为“Customer”的非常大的表的示例：

CustomerID | LastName | FirstName | Address | City|
-------------|----------|-----------|---------|------|
1520年|盖尔|弗朗西斯科| XPTO |伦敦|**
2214 |桑托斯|安东尼奥|图多|波尔图|
3998 | Freix | Luís | IUPO |魁北克|
1520年|盖尔|弗朗西斯科|斯普托|罗马|**
5691 |安东|安娜|蒂迪|里斯本|
1520年|盖尔|弗朗西斯科|斯普托|罗马|**

从这个小示例可以看出，对于同一个客户（

CustomerID=1520

），City列中的值不同

例如，在这种情况下，所需的输出为：

 CustomerID | City |
 -----------|------|
 1520       |London|
 1520       |Rome  |

我尝试开发一个查询，返回在City列中具有不同值的CustomerID

SELECT CustomerID, City 
FROM (SELECT CustomerID, COUNT(DISTINCT City) FROM Customer GROUP BY CustomerID) 
WHERE City > 1

---

有人能帮我找出我开发的查询有什么问题吗？

您可以使用

HAVING

来筛选：

SELECT *
FROM Customer
WHERE CustomerID IN(SELECT CustomerID
                    FROM Customer 
                    GROUP BY CustomerID
                    HAVING COUNT(DISTINCT City) > 1);

---

您可以使用

HAVING

来筛选：

SELECT *
FROM Customer
WHERE CustomerID IN(SELECT CustomerID
                    FROM Customer 
                    GROUP BY CustomerID
                    HAVING COUNT(DISTINCT City) > 1);

---

如果需要城市，您可以使用

exists

：

select c.*
from customers c
where exists (select 1
              from customers c2
              where c2.customerid = c.customerid and c2.city <> c.city
             );

---

如果需要城市，您可以使用

exists

：

select c.*
from customers c
where exists (select 1
              from customers c2
              where c2.customerid = c.customerid and c2.city <> c.city
             );

---

您可以使用以下选项：

SELECT CustomerID, City
FROM Customer
WHERE CustomerID IN (
  SELECT CustomerID
  FROM Customer
  GROUP BY CustomerID
  HAVING COUNT(DISTINCT City) > 1
)
GROUP BY CustomerID, City;

结果:

| CustomerID | City   |
|------------|--------|
| 1520       | London |
| 1520       | Rome   |

---

您可以使用以下选项：

SELECT CustomerID, City
FROM Customer
WHERE CustomerID IN (
  SELECT CustomerID
  FROM Customer
  GROUP BY CustomerID
  HAVING COUNT(DISTINCT City) > 1
)
GROUP BY CustomerID, City;

结果:

| CustomerID | City   |
|------------|--------|
| 1520       | London |
| 1520       | Rome   |

---

@安娜。你不接受这个答案有什么原因吗？它应该比在中使用group by@Anna>的更有效。你不接受这个答案有什么原因吗？它应该比在中使用分组方式的更有效。