The algorithm and flowchart are two types of tools to explain the process of a program. In this page, we discuss the differences between an algorithm and a flowchart and how to create a flowchart to illustrate
一般在查询时使用了聚合函数,于是直接从索引树里获取数据,而不用查询表中的记录。 explainselectmin(id)fromtb_book; const: 在进行查询时,查询的条件,使用了主键列或者唯一索引列的值与常量进行比较,这种性能是非常快的,所以是const system: 是const的特殊情况,一般在衍生表里,直接匹配一条记录,就是system EXPLAIN...
11 No matching min/max row 没有任何能满足例如 SELECT MIN(...) FROM ... WHERE condition 中的condition的行 12 no matching row in const table 对于关联查询,存在一个空表,或者没有行能够满足唯一索引条件 13 No matching rows after partition pruning 对于DELETE或UPDATE语句,优化器在partition pruning(...
|1| SIMPLE |testa| const |PRIMARY,idx_name| PRIMARY |4| const |1| NULL |+---+---+---+---+---+---+---+---+---+---+1rowinset# 下面虽然name有索引,但是查询的列cusno没有索引,这时mysql计划possible_keys有索引,但实际key未走索引,若果cusno换成有索引的列,参照下面。mysql> expl...
When an SQL statement is delivered, the QO compares the costs of redistribution and broadcast, and then generates an execution plan based on the algorithm. Optimization suggestion: If the table that you want to query is small and the instance contains a small number of shards, such as 5 ...
EXPLAIN - Scan Nodes This section lists the different scan nodes in Postgres. Note that some nodes are general and several alternatives may be available in a particular query, with the actual node determined by the planning algorithm outlined above (e.g., an Index Scan and a Sequential Scan)...
See Batched Key Access Joins, for information about the Batched Key Access algorithm. Using MRR (JSON property: message) Tables are read using the Multi-Range Read optimization strategy. See Section 10.2.1.11, “Multi-Range Read Optimization”. Using sort_union(...), Using union(...)...
2822 MIN columns. 2824 MAX columns. 2826 SUM columns. 2828 COUNT columns. 2830 AVERAGE columns. 2910 Subselect number of the inner subselect. 2912 Nested level of the inner subselect. 2914 Subselect number of the materialized view containing the inner subselect. 2916 Nested level of the materiali...
See Batched Key Access Joins, for information about the Batched Key Access algorithm. Using MRR (JSON property: message) Tables are read using the Multi-Range Read optimization strategy. See Section 10.2.1.11, “Multi-Range Read Optimization”. Using sort_union(...), Using union(...)...
Euclid’s algorithm C# Event method called twice EventHandler: Is event always in the same thread? And what about thread safety? Events within BackgroundWorker.DoWork() - Calls are illegal examples using C# with Ta Lib or others Examples, or guiidance on sending a docx file to a therma...