从多次的测试中可以发现,不能滥用Outer Apply 来代替Left Outer Join。 其实在联机帮助中Apply 定义是这样: ”使用 APPLY 运算符可以为实现查询操作的外部表表达式返回的每个行调用表值函数。表值函数作为右输入,外部表表达式作为左输入。通过对右输入求值来获得左输入每一行的计算结果,生成的行被组合起来作为最终输出。
从多次的测试中可以发现,不能滥用Outer Apply 来代替Left Outer Join。 其实在联机帮助中Apply 定义是这样: ”使用 APPLY 运算符可以为实现查询操作的外部表表达式返回的每个行调用表值函数。表值函数作为右输入,外部表表达式作为左输入。通过对右输入求值来获得左输入每一行的计算结果,生成的行被组合起来作为最终输出。
OUTER APPLY 的意思是“外部应用”,与 CROSS APPLY的原理一致,只是在匹配失败时,左表与右表也将合并为一条记录输出,不过右表的输出字段为 null。(与 LEFT OUTER JOIN 类似) CROSS APPLY 与 INNER JOIN 的区别 CROSS APPLY 可以根据当前左表的当前记录去查询右表,但是 INNER JOIN 不可以,INNER JOIN 是根据左...
LEFT JOIN and LEFT OUTER JOIN in SQL are identical, with no functional difference between them. See examples of how these joins work in SQL queries.
Sqlserver之 CROSS APPLY 与 OUTER APPLY <--> INNER/LEFTJOIN –用OUTER APPLYselect b.* FROM a表 aOUTER APPLY(select TOP(1) * from b表 WHERE [Name] = a.[AName] ORDER BY BNo desc) b总结:1. 理解 CROSS APPLY 与 OUTER APPLY1) CROSS APPLY 的意思是“交叉应用”,在查询时首先查询左表,...
LeftOuterJoin和OuterApply性能比较 2009-03-26 23:12 −建立测试环境: 建立一个表Department和Employee,并向Department插入50W条记录,向Employee插入200W条记录, 我们就拿【统计DepartmentID 从150000 至380000的每一个Department有多少个Employee】这样一问题 ... ...
In particular, the seek into Table2 should be a seek on both id and ShardKey, but in the LEFT OUTER JOIN WHERE OR IS NULL version it is a seek only on id and a subsequent Filter operator tests all matching rows in order to apply the appropriate ShardKey restriction. This difference ma...
left join: 1 big operation being reused by all inserted row outer apply: 1 small operation being executed once per inserted row my question is, at this point i don't know enough about execution plan to decide which kind of join i should keep, left join or outer apply? this is bein...
Hive的Join的文档说明地址： https://cwiki.apache.org/confluence/display/Hive/LanguageManual%2BJoins ...
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