Question

我有6个mysql数据库，其表名相同，例如users_table，字段为email_address，现在我想从任何一个数据库表中丢失所有6个db中的email_address。

请给我一些建议。

Answer 1

此选项会选择其中一个数据库中缺少的所有电子邮件，并指出它们所在的数据库。

SELECT email, GROUP_CONCAT(db_Name) AS emailIsOnlyIn FROM (
   SELECT 'db1' as db_Name, email FROM db1.yourTable
   UNION ALL
   SELECT 'db2' as db_Name, email FROM db2.yourTable
   UNION ALL
   SELECT 'db3' as db_Name, email FROM db3.yourTable
   UNION ALL
   SELECT 'db4' as db_Name, email FROM db4.yourTable
   UNION ALL
   SELECT 'db5' as db_Name, email FROM db5.yourTable
   UNION ALL
   SELECT 'db6' as db_Name, email FROM db6.yourTable
) subquery_alias
GROUP BY email
HAVING COUNT(DISTINCT db_name) < 6;

如果您想知道哪个数据库丢失了电子邮件，那就更复杂了：

SELECT
*
FROM (
   SELECT email FROM db1.yourTable
   UNION 
   SELECT email FROM db2.yourTable
   UNION 
   SELECT email FROM db3.yourTable
   UNION 
   SELECT email FROM db4.yourTable
   UNION
   SELECT email FROM db5.yourTable
   UNION 
   SELECT email FROM db6.yourTable
) sq,
    (    SELECT 'db1' as db_Name2
       UNION ALL
       SELECT 'db2' as db_Name2
       UNION ALL
       SELECT 'db3' as db_Name2
       UNION ALL
       SELECT 'db4' as db_Name2
       UNION ALL
       SELECT 'db5' as db_Name2
       UNION ALL
       SELECT 'db6' as db_Name2
   )dummy
WHERE NOT EXISTS (SELECT 1 FROM (
   SELECT 'db1' as db_Name, email FROM db1.yourTable
   UNION ALL
   SELECT 'db2' as db_Name, email FROM db2.yourTable
   UNION ALL
   SELECT 'db3' as db_Name, email FROM db3.yourTable
   UNION ALL
   SELECT 'db4' as db_Name, email FROM db4.yourTable
   UNION ALL
   SELECT 'db5' as db_Name, email FROM db5.yourTable
   UNION ALL
   SELECT 'db6' as db_Name, email FROM db6.yourTable
   ) subquery_alias
 WHERE sq.email = subquery_alias.email AND subquery_alias.db_Name = dummy.db_Name2
)

这是展示概念证明的sqlfiddle

从6个不同的mysql数据库同步用户表数据

1 个答案: