Mysql 基于一列删除重复项，并将具有值的行保留在不同的列中，如果没有，则保留ID最低的行

在Google Cloud上使用MySQL 5.7，我试图基于EmailAddress列消除MySQL数据的重复数据，但有些行在FullName列中有值，有些行没有。我想保留那些在FullName列中有值的行，但是如果EmailAddress值的行中没有一行是FullName值，那么只保留ID号最低的第一列-主键的副本

我最后将其分解为两个单独的查询，一个是首先删除FullName列中没有值的行，如果FullName列中有另一个重复的行，则删除该行：

DELETE
FROM customer_info
WHERE id IN
(
 SELECT * 
 FROM
    (   
     SELECT c1.id
     FROM customer_info c1
            INNER JOIN customer_info c2 on c1.EmailAddress=c2.EmailAddress and c1.id!=c2.id
     WHERE 
            (trim(c1.FullName)='' or c1.FullName is NULL)
            and c2.FullName is not NULL
            and length(trim(c2.FullName))!=0
    ) t
)

DELETE
FROM customer_info
WHERE id IN
(
 SELECT * 
 FROM
    (   
     SELECT c1.id
     FROM customer_info c1
            INNER JOIN customer_info c2 on c1.EmailAddress=c2.EmailAddress and c1.id>c2.id
    ) t
)

以及另一个查询，用于删除在FullName列中找不到值的ID较大的行：

DELETE
FROM customer_info
WHERE id IN
(
 SELECT * 
 FROM
    (   
     SELECT c1.id
     FROM customer_info c1
            INNER JOIN customer_info c2 on c1.EmailAddress=c2.EmailAddress and c1.id!=c2.id
     WHERE 
            (trim(c1.FullName)='' or c1.FullName is NULL)
            and c2.FullName is not NULL
            and length(trim(c2.FullName))!=0
    ) t
)

DELETE
FROM customer_info
WHERE id IN
(
 SELECT * 
 FROM
    (   
     SELECT c1.id
     FROM customer_info c1
            INNER JOIN customer_info c2 on c1.EmailAddress=c2.EmailAddress and c1.id>c2.id
    ) t
)

这是可行的，但不是真的。有一次，当我让它整夜运行以获取较小的数据段时，它工作了，当我醒来时，出现了一个错误，但我查看了数据，它就完成了

<>我在查询中漏掉了一些东西，这使得它效率很低，或者只是因为这类查询的过程是否平淡无奇，而在我的代码中没有可能会做出切实的改进呢？我已经将一个Google Cloud SQL实例最大化为db-n1-highmem-32大小，内存为32 GB，存储空间为1000 GB，但在运行了一个小时后，它仍然阻塞并抛出了一个2013年的错误。我总共需要做300多万行

例如，这：

id | FullName      | EmailAddress            |
----------------------------------------------
1  | John Doe      | john.doe@email.com      |
2  | null          | janedoe@box.com         |
3  | null          | billybob@bobby.com      |
4  | null          | john.doe@email.com      |
5  | John Lennon   | jlennon@yoohoo.com      |
6  | null          | james.smith@coolmail.com|
7  | null          | billybob@bobby.com      |
8  | Jane Doe      | janedoe@box.com         |

这将导致：

id | FullName      | EmailAddress            |
----------------------------------------------
1  | John Doe      | john.doe@email.com      |
3  | null          | billybob@bobby.com      |
5  | John Lennon   | jlennon@yoohoo.com      |
6  | null          | james.smith@coolmail.com|
8  | Jane Doe      | janedoe@box.com         |

在这种情况下，使用exists可能更简单

delete
from customer_info c
where (trim(c.FullName)='' or c.FullName is null)
  and exists (   
     select 1
     from customer_info i
     where i.Email = c.EmailAddress 
      and trim(i.FullName)>'' 
  )

delete
from customer_info c
where exists (
     select 1
     from customer_info i
     where i.Email = c.EmailAddress 
       and i.id < c.id
  )

---

你能提供一个样本数据的例子吗？@Suraz我已经在原始帖子中添加了这个例子。