Using sort_union(…), Using union(…), Using intersect(…) 这些指示索引扫描如何合并为index_merge连接类型。 (参考https://dev.mysql.com/doc/refman/5.7/en/index-merge-optimization.html) 索引合并交叉口访问算法(The Index Merge Intersection Access Algorithm): index intersect merge就是多个索引条件扫描...
index merge 的思路实际上就是 multiple range scans and merge result into one, 主要支持三种对结果集聚合的方式,intersections交集,unions并集,sort-union The difference between the sort-union algorithm and the union algorithm is that the sort-union algorithm must first fetch row IDs for all rows and ...
There are 2 steps to solve this one. Solution Share Step 1 ANSWER : The time complexity of the merge sort algorithm is mainly determined by the number of recursive cal...View the full answer Step 2 Unlock Answer UnlockPrevious question Ne...
The Modified filesort Algorithm 较Original改变的地方是, 在第2步记录的是sort key和涉及到的其它列, 即<sort_key, additional_fields>, 不是row ID了. 第3步完成后, 就可得到结果了. 这个算法中<sort_key, additional_fields>占用空间比<sort_key, rowid>要大, 若排序数据量很大的情况下, 会频繁写临时...
Merge Join mjoin Also used for inner joins and outer joins (for join tables that are both distributed and sorted on the joining columns). Typically the fastest Amazon Redshift join algorithm, not including other cost considerations. AGGREGATION: Operators and steps used for queries that involve...
本文来自我的github pages博客http://galengao.github.io/ 即www.gaohuirong.cn 摘要: 本篇是根据官网中的每个一点来翻译、举例、验证的;英语不好,所以有些话语未必准确,请自行查看官网,若有些点下面没有例子的是因为当时一下子没有想出那么多来,如果大家
The join order is determined by using an algorithm, and an optimal execution plan is generated. This may increase the QO overhead during multi-table join. query The execution plan is generated based on SQL statements. The QO does not make any changes. This value is applicable and helps de...
(Block Nested Loop) indicates use of the Block Nested-Loop algorithm and (Batched Key Access) indicates use of the Batched Key Access algorithm. That is, the keys from the table on the preceding line of the EXPLAIN output are buffered, and the matching rows are fetched in batches from ...
7 index_merge:此类型表示使用了索引合并优化,表示一个查询里面用到了多个索引 8 unique_subquery:该类型和eq_ref类似,但是使用了IN查询,且子查询是主键或者唯一索引。例如: 代码语言:javascript 复制 valueIN(SELECTprimary_keyFROMsingle_tableWHEREsome_expr) ...
DFELabelPropagationAlgo – Explain operator for invocations of the Label Propagation algorithm, which is used for community detection. DFELoopSubQuery – This is a non-blocking operation that acts as a wrapper for a subquery, allowing it to be run repeatedly for use in loops. DFEMergeChunks –...