ss_users

用户ID
的firstName
lastName
电子邮件

我想获得所有所有者，备份和经理的姓名/电子邮件列表。

我正在使用下面的查询，但是想知道是否有更有效的方法来查询表格。

工作查询：

SELECT DISTINCT email,
                ( firstName + ' ' + lastName ) AS userFull,
                lastName
FROM   common_products cp
       LEFT OUTER JOIN ss_users u
                    ON u.userID = cp.owner_uid
UNION
SELECT DISTINCT email,
                ( firstName + ' ' + lastName ) AS userFull,
                lastName
FROM   common_products cp
       LEFT OUTER JOIN ss_users u
                    ON u.userID = cp.backup_uid
UNION
SELECT DISTINCT email,
                ( firstName + ' ' + lastName ) AS userFull,
                lastName
FROM   common_products cp
       LEFT OUTER JOIN ss_users u
                    ON u.userID = cp.manager_uid

是否有更优化的方式来查询数据库？

Answer 1

我怀疑这个版本可能会更快：

select u.email, (u.firstName+ ' '+u.lastName) AS userFull, u.lastName
from ss_users u
where exists (select 1 from common_products cp where u.userID = cp.owner_uid) or
      exists (select 1 from common_products cp where u.userID = cp.backup_uid) or
      exists (select 1 from common_products cp where u.userID = cp.manager_uid);

然后为了获得最佳效果，请添加三个索引：common_products(owner_uid)，common_products(backup_uid)和common_products(manager_uid)。

这将消除重复消除（因为您使用的是union），而exists应该至少与join一样快。

Answer 2

我要简化它，但JOIN是重要的部分。我会留给你调整SELECT部分。

SELECT DISTINCT owner.email AS owner_email, backup.email AS back_email, manager.email AS man_email
FROM common_product cp LEFT JOIN ss_users owner on owner.userID = cp.owner_uid
LEFT JOIN ss_users backup on backup.userID = cp.backup_uid
LEFT JOIN ss_users manager on manager.userID = cp.manager_uid

Answer 3

确保common_products的owner_uid，backup_uid和manager_uid字段以及ss_users的userID字段都有索引，您可以通过包含索引所需的列来进一步提高性能。

SELECT DISTINCT
    user_owner.email [OwnerEmail],user_owner.firstName + ' ' + user_owner.lastName [OwnerUserFull], user_owner.lastName [OwnerLastName],
    user_backup.email [BackupEmail],user_backup.firstName + ' ' + user_backup.lastName [BackupUserFull], user_backup.lastName [BackupLastName],
    user_manager.email [ManagerEmail],user_manager.firstName + ' ' + user_manager.lastName [ManagerUserFull], user_manager.lastName [ManagerLastName]
FROM   common_products cp
LEFT OUTER JOIN ss_users user_owner ON user_owner.userID = cp.owner_uid
LEFT OUTER JOIN ss_users user_backup ON user_backup.userID = cp.backup_uid
LEFT OUTER JOIN ss_users user_manager ON user_manager.userID = cp.manager_uid

Answer 4

我已经习惯了SQL fu，但我认为这应该有效：

SELECT DISTINCT email,
    (firstName+ ' '+lastName) AS userFull,
    lastName 
FROM common_products cp 
INNER JOIN  ss_users u 
ON (u.userID = cp.owner_uid OR u.userID = cp.backup_uid OR u.userID = cp.manager_uid)

优化SQL连接单列，在另一个表中包含多个列

common_products

ss_users

4 个答案: