图6.Not In Vs Not Exists 由图6可以看出,Not In的执行成本几乎是Not Exists的3倍,仅仅是由于SQL Server需要确认允许Null列中是否存在Null。根据图3中Not In的等价形式,我们完全可以将Not In转换为等价的Not Exist形式,如图7所示。 image 图7.Not In转换为Not Exists 我们来对比图7
图6.Not In Vs Not Exists由图6可以看出，Not In的执行成本几乎是Not Exists的3倍，仅仅是由于SQL Server需要确认允许Null列中是否存在Null。根据图3中Not In的等价形式，我们完全可以将Not In转换为等价的Not Exist形式，如图7所示。图7.Not In转换为Not Exists我们来对比图7和其等价Not In查询的...
not in和not exists是不等价的, 一般情况下建议使用not exists, 需要注意关联字段是否为null,主查询关联字段值为null时的记录是否需要返回. 19. 用NOT EXISTS替代NOT IN 在子查询中,NOT IN子句将执行一个内部的排序和合并. 无论在哪种情况下,NOT IN都是最低效的 (因为它对子查询中的表执行了一个全表遍历)...
http://www.cnblogs.com/mytechblog/articles/2105785.html NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: SQL Server at EXPLAIN EXTENDED https://explainextended.com/2009/09/15/not-in-vs-not-exists-vs-left-join-is-null-sql-server/ 在sql语句多表连接中,in、exists、join那个效率更高一点。...
InSQL Server,NOT EXISTSandNOT INpredicates are the best way to search for missing values, as long as both columns in question areNOT NULL. They produce the safe efficient plans with some kind of anAnti Join. LEFT JOIN / IS NULLis less efficient, since it makes no attempt to skip the ...
not in 和not exists 如果查询语句使用了not in 那么内外表都进行全表扫描,没有用到索引;而not extsts 的子查询依然能用到表上的索引。所以无论那个表大,用not exists都比not in要快 7. 选择最有效率的表名顺序(只在基于规则的优化器中有效) ORACLE的解析器按照从右到左的顺序处理FROM子句中的表名,FROM...
通过以上两条SQL语句的比较我们可以明白,NOT EXISTS直接具备了差集运算的功能。 全称量化(1):习惯“肯定⇔双重否定”之间的转换 接下来我们练习一下如何使用EXISTS谓词来表达全称量化,这是EXISTS的用法中很具有代表性的一个用法。通过这一部分内容的学习,希望大家能习惯从全称量化“所有的行都××”到其双重否定“不...
Hi,in a office network, i have a virtual machine win 2003, and install sql server 2005 on it, but i can not access to this sql from other client (ip or name not differ), and i receive message as "sql server dose not exist or access denied" please help me, thanks. Anonymo...
The jobs isn't working! When I start a job, I had the follow message; "Error 2202: Job oXxxxxxxxxx does not exist in the job cache." I tried to restart the SQL services, but without success! My environment is Windows 2003 Server! Could you help me? Regards Erick...
CREATE TABLE IF NOT EXISTS customers ( ... ) 1. PostgreSQL代码更加简单,简洁和完善。SQL Server代码绝对是维护的噩梦。 几个例子: SQL Server -- This throws an error if the table doesn’t exist DROP TABLE [dbo].[customers] -- This is how you do it in SQL Server 2014 and older IF...