否定选择SQL查询

Question

我的任务是从我们的sql数据库中返回一个否定选择.我会尽可能地定义标准.到目前为止,我还没有制作出有效的查询.

业务表

[公交车名称] [公交车ID]

活动表

[活动ID] [巴士ID]

活动扩展表

[分机ID] [活动ID] [巴士ID]

我需要在关联表中没有该企业ID#记录的所有企业的企业名称.简单地说,所有企业都没有活动.业务ID可以存在于一个或两个关联表中.

在尝试使用连接进行查询而不是在语句中存在或不存在时,这导致我几个小时的麻烦.没有成功.

有任何想法吗？

Answer 1

运用 NOT IN

SELECT b.*
  FROM BUSINESS b
 WHERE b.business_id NOT IN (SELECT a.business_id
                               FROM ACTIVITY a)
   AND b.business_id NOT IN (SELECT ae.business_id
                               FROM ACTIVITY_EXTENSION ae)

运用 NOT EXISTS

SELECT b.*
  FROM BUSINESS b
 WHERE NOT EXISTS (SELECT NULL 
                     FROM ACTIVITY a
                    WHERE a.business_id = b.business_id)
   AND NOT EXISTS (SELECT NULL 
                     FROM ACTIVITY_EXTENSION ae
                    WHERE ae.business_id = b.business_id)

运用 LEFT JOIN/IS NULL

   SELECT b.*
     FROM BUSINESS b
LEFT JOIN ACTIVITY a ON a.business_id = b.business_id
LEFT JOIN ACTIVITY_EXTENSION ae ON ae.business_id = b.business_id
    WHERE a.business_id IS NULL
      AND ae.business_id IS NULL

结论

因为关系是外键(business_id),所以假设它们都不为null是安全的.在这种情况下,NOT IN并且NOT EXISTS是寻找在SQL Server中丢失价值的最佳手段.LEFT JOIN/IS NULL效率较低 - 您可以在本文中阅读更多相关内容.

Answer 2

SELECT * FROM businesses WHERE business.id NOT IN (SELECT DISTINCT business_id FROM activities)