多个表SQL Server中的多次更新和删除

Question

我有四个表，分别是 City、Location、Customer 和 Shop。设计此数据库的人已使主键自动递增。因此，DB超时存在冗余数据。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           |

预期表格：

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           |

如您所见，到处都有重复记录，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

这是删除 1 个重复的 City，City 表中大约有 1300 个重复。有没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性更新整个表格。在您的情况下，存在具有重复值的另一行。

-- (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

-- ...

其余的查询可以类比这些例子

Answer 2

不完美，但应该可以从这里开始工作

declare @City table (ID_city int primary key, City varchar(10));
insert into  @city values 
       (1, 'Chennai')
     , (2, 'Benagluru')
     , (3, 'Chennai')
     , (4, 'Delhi')
     , (5, 'Chennai')
     , (6, 'Benagluru');
--select * from @city c order by c.City, c.ID_city;

declare @Location table (ID_Location int primary key, ID_City int, zip char(4))
insert into @Location values 
       (1, 1, '0001') 
     , (2, 2, '0011')
     , (3, 1, '0002')
     , (4, 3, '0021')
     , (5, 1, '0003')
     , (6, 2, '0012')
     , (7, 1, '0001');  --duplicate
--select * from @Location l order by l.ID_Location;

declare @Customer table (Cust_ID int primary key, ID_Location int)
insert into @Customer values
       (1, 1)
     , (2, 3)
     , (3, 5)
     , (4, 2)
     , (5, 7);
--select * from @Customer;

declare @Shop table (Shop_ID int primary key, ID_Location int) 
insert into @Shop values 
       (1, 1)
     , (2, 2)
     , (3, 6)
     , (4, 3)
     , (5, 7);
--select * from @Shop s order by s.Shop_ID;

 declare @LocationMap table (ID_Location int primary key, ID_City int, zip char(4), cnt int, rn int)
 insert into @LocationMap
 select l.* 
      , count(*)     over (partition by zip) as cnt 
      , ROW_NUMBER() over (partition by zip order by ID_Location) as rn 
   from @Location l;
--select * from @LocationMap where cnt > 1 order by zip, rn;

declare @CityMap table (ID_city int primary key, City varchar(10), cnt int, rn int)
insert into @CityMap 
select c.* 
     , count(*)     over (partition by City) as cnt 
     , ROW_NUMBER() over (partition by City order by City, ID_city) as rn 
 from @City c;
--select * from @CityMap m where m.cnt > 1 order by m.City, m.ID_city;

update c 
set c.ID_Location = f.ID_Location
from @Customer c
join @LocationMap m 
  on m.ID_Location = c.ID_Location
 and m.rn > 1
join @LocationMap f 
  on f.ID_City = m.ID_City
 and m.rn = 1; 
select c.* from @Customer c order by c.Cust_ID

update s 
set s.ID_Location = f.ID_Location
from @shop s 
join @LocationMap m 
  on m.ID_Location = s.ID_Location
 and m.rn > 1
join @LocationMap f 
  on f.zip = m.zip 
 and m.rn = 1; 
select s.* from @shop s order by s.Shop_ID;

--select l.* from @Location l order by l.ID_Location;
update l 
set l.ID_City = f.ID_City
from @Location l
join @CityMap m 
  on m.ID_city = l.ID_City 
 and m.rn > 1
join @CityMap f 
  on f.City = m.City
 and f.rn = 1; 
select l.* from @Location l order by l.ID_Location;

 delete l 
 from @Location l 
 join @LocationMap m
   on l.ID_Location = m.ID_Location 
  and m.rn > 1;
select * from @Location l order by l.ID_Location;

 delete c 
 from @City c
 join @CityMap m
   on c.ID_city = m.ID_city 
  and m.rn > 1;
select * from @City c order by c.ID_city;