sql - 多个表中的多个更新和删除 SQL Server

Question

我有四个表，即城市、位置、客户和商店。设计此数据库的人已将主键设置为自动递增。结果导致DB超时有冗余数据。我正在尝试清理数据库，但更新和删除行需要很长时间。表格示例如下所示:

Table 1: City: ID_city(PK)
| City      | ID_City |
|-----------|---------|
| Chennai   | 1       |
| Benagluru | 2       |
| Chennai   | 3       |
| Delhi     | 4       |
| Chennai   | 5       |
| Bengaluru | 6       |

Table 2: Location: ID_Location(PK), ID_City(FK)
| Zip  | ID_location        | ID_City |
|------|--------------------|---------|
| 0001 | 1                  | 1       |
| 0011 | 2                  | 2       |
| 0002 | 3                  | 1       |
| 0021 | 4                  | 3       |
| 0003 | 5                  | 1       |
| 0012 | 6                  | 2       |
| 0001 | 7 (duplicate of 1) | 1       |

Table 3: Customer: Cust_ID(PK), ID_Location(FK)
| Cust_ID | ID_location |
|---------|-------------|
| 1       | 1           |
| 2       | 3           |
| 3       | 5           |
| 4       | 2           |
| 5       | 7           |

Table 4: Shop: Shop_ID(PK), ID_Location(FK)
| Shop_ID | ID_location |
|---------|-------------|
| 1       | 1           |
| 2       | 2           |
| 3       | 6           |
| 4       | 3           |
| 5       | 7           |

期望表:

Table 1: City: ID_city(PK)
| City      | ID_City |
|-----------|---------|
| Chennai   | 1       |
| Benagluru | 2       |
| Delhi     | 4       |

Table 2: Location: ID_Location(PK), ID_City(FK)
| Zip  | ID_Location | ID_City |
|------|-------------|---------|
| 0001 | 1           | 1       |
| 0011 | 2           | 2       |
| 0002 | 3           | 1       |
| 0021 | 4           | 1       |
| 0003 | 5           | 1       |
| 0012 | 6           | 2       |

Table  3: Customer: Cust_ID(PK), ID_Location(FK)
| Cust_ID | ID_Location |
|---------|-------------|
| 1       | 1           |
| 2       | 3           |
| 3       | 5           |
| 4       | 2           |
| 5       | 1           |

Table 4: Shop: Shop_ID(PK), ID_Location(FK)
| Shop_ID | ID_Location |
|---------|-------------|
| 1       | 1           |
| 2       | 2           |
| 3       | 6           |
| 4       | 3           |
| 5       | 1           |

如你所见，到处都有重复的记录，需要 3 个更新语句(使用连接)和 2 个删除语句才能删除 1 个重复的城市。 有没有办法减少执行此任务的 SQL 语句的数量？

我写的查询是:

1. 更新客户集 ID_location = 1，其中 Cust_ID = 5
2. 更新商店集 ID_location = 1，其中 Shop_ID = 5
3. 从 ID_location = 7 的位置删除
4. 更新位置集 ID_City = 1，其中 ID_City = 3 或 ID_City = 5
5. 从 ID_Location = 3 或 ID_Location = 5 的城市中删除

这是为了删除 1 个重复的城市，城市表中大约有 1300 个重复的城市。是否有一种简单的方法来检查重复项、更新并最终删除？

Answer 1

您可以根据条件一次更新整个表。在您的情况下，存在另一行具有重复值。

-- (1) UPDATE DUPLICATE CITIES ON LOCATION
UPDATE l SET l.Id_City = mstr.Id_City
-- SELECT c.Id_City oldId, mstr.Id_City newId  -- Check this for your convenience
FROM [Location] l
    INNER JOIN City c ON c.Id_City = l.Id_City 
    INNER JOIN (
        SELECT City, MIN(Id_City) Id_City -- KEEP FIRST ONLY
        FROM City
        GROUP BY City
        HAVING COUNT(1) > 1
    ) mstr ON mstr.City = c.City
        AND mstr.Id_City < Id_City

-- (2) DELETE DUPLICATE CITIES
DELETE c
-- SELECT c.Id_City oldId, mstr.Id_City newId  -- Check this for your convenience
FROM City c
    INNER JOIN (
        SELECT City, MIN(Id_City) Id_City -- KEEP FIRST ONLY
        FROM City
        GROUP BY City
        HAVING COUNT(1) > 1
    ) mstr ON mstr.City = c.City
        AND mstr.Id_City < Id_City

-- ...

其余的查询可以模拟这些例子