mysql - 从 6 个不同的 mysql 数据库同步用户表数据

Question

我有 6 个具有相同表名的 mysql 数据库，例如带有字段 email_address 的 users_table，现在我想从所有 6 个数据库中获取任何一个数据库表中缺少的 email_address。

请给我一些相同的建议。

Answer 1

这一个选择在其中一个数据库中丢失的所有电子邮件，并指出它们存在于哪个数据库中。

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;

如果您想知道电子​​邮件丢失在哪个数据库中，则要复杂一些：

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
)

• 这是一个演示概念证明的sqlfiddle