WebJun 5, 2024 · You want records in the MView which don't match rows in the sub-query - an anti-join. In your query that would be a LEFT OUTER JOIN. However, the optimizer has decided it would be more efficient to gather the result set of the sub-query first than evaluate the anti-join on the MView, which is a right outer join. WebWhen used with two inputs, Hash Match implements nine of the ten logical join operations: inner join; left, right, and full outer join; left and right semi and anti semi join; as well as union. The Union logical operation does require that the probe input is guaranteed free of duplicates, either because of trusted constraints on the base input ...

数据库三种基本连接操作(HASH JOIN MERGE JOIN …

WebMar 7, 2015 · Hash Join是做大数据集连接时的常用方式，优化器使用两个表中较小（相对较小）的表利用Join Key在内存中建立散列表，然后扫描较大的表并探测散列表，找出与Hash表匹配的行。 这种方式适用于较小 … WebApr 10, 2024 · 优化 ：MySQL 查询优化器在这个阶段会尝试找到最佳的执行计划。. 它会根据表的大小、索引、连接顺序等因素来选择最佳的连接算法。. 对于这个例子，优化器可能会选择 Nested-Loop Join（嵌套循环连接），因为这通常是最适合小型表连接的算法。. 执行 … church bell sound system

数据库 - 全面解读PostgreSQL和Greenplum的Hash Join - 全球首个开源、多云大数据分析平台Greenplum ...

WebAug 21, 2024 · hash join 就是 当两个或者多个表join 查询时，基于其中一个表 (驱动表)在内存构建一个哈希表，然后一行一行读另一个表 (被驱动表)，计算其哈希值到内存哈希表 … Web示例：执行下面SQL语句，a表倾斜或b表倾斜都无法触发该优化。 select aid FROM a FULL OUTER JOIN b ON aid=bid; 不支持LEFT OUTER JOIN的右表倾斜处理。 示例：执行下面SQL语句，b表倾斜无法触发该优化。 select aid FROM a LEFT OUTER JOIN b ON aid=bid; 不支持RIGHT OUTER JOIN的左表倾斜处理。 WebA hash join can also be used when there are one or more indexes that can be used for single-table predicates. A hash join is usually faster than and is intended to be used in such cases instead of the block nested loop algorithm (see Block Nested-Loop Join Algorithm) employed in previous versions of MySQL. detroit and mackinac railway