UNION RESULT UNION的结果 。 SUBQUERY 子查询中的第一个SELECT语句。 DEPENDENT SUBQUERY 子查询中的第一个SELECT语句,同时该语句依赖外部的查询。 DERIVED 派生表。位于form中的子查询,MySQL会将其结果存放在一个临时表中,即这里的派生表。 MATERIALIZED 物化子查询,优化 FROM/IN 子句中的子查询。 UNCACHEABLE SUB...
SIMPLE:查询中不包含子查询或者UNION b.查询中若包含任何复杂的子部分,最外层查询则被标记为:PRIMARY c.在SELECT或WHERE列表中... …… 用于分区表的EXPLAIN 二.执行计划包含的信息1.id: 包含一组数字,表示查询中执行select子句或操作表的顺序,如: id相同,执行顺序由上至下。如果是子查询,id mysql_高级_索引...
/* No work if empty tlist (this occurs eg in bitmap indexscans) */ if (plan->targetlist == NIL) return; /* The tlist of an Append isn't real helpful, so suppress it */ if (IsA(plan, Append)) return; /* Likewise for MergeAppend and RecursiveUnion */ if (IsA(plan, MergeAp...
分析你的查询语句或是表结构的性能瓶颈。 (一)ID (二)select_type列:数据读取操作的操作类型 1、SIMPLE:简单的select 查询,SQL中不包含子查询或者UNION。 2、PRIMARY:查询中包含复杂的子查询部分,最外层查询被标记为PRIMARY 3、... Mysql中 EXPLAIN (执行计划)...
For example, if a hash aggregate operator is used in the first step of a query plan, full data of downstream operators is required to create a hash table for an aggregate operation. For common queries with filter conditions, data is calculated and returned in real time. In this scenario, ...
Eurostat is the statistical office of the European Union33. The variables span six macro areas that have been found in literature to be relevant in relation to the spread of viruses: economy, education, population, healthcare, primary sector and mobility. Although the data is made available by...
What is the primary advantage of setting up a corporation relative to other forms of business organization? a. Double taxation. b. Higher regulatory. c. Requirements labor union rules. d. Limited liability. How would each of the following changes te...
Explain in detail using an example. Evaluate whether the following statements are true, false, or uncertain. a. A labor union decreases efficiency and wage rate. b. A minimum wage policy increases efficiency and employment. 1. True or F...
WITH p AS ( SELECT plan_hash_value FROM gv$sql_plan WHERE sql_id = TRIM('&&sql_id.') AND other_xml IS NOT NULL UNION SELECT plan_hash_value FROM dba_hist_sql_plan WHERE sql_id = TRIM('&&sql_id.') AND other_xml IS NOT NULL ), ...
Node Type is a string with a step name. Plans is an array with child step descriptions. Other optional keys may be added depending on node type and settings. Example: EXPLAIN json = 1, description = 0 SELECT 1 UNION ALL SELECT 2 FORMAT TSVRaw;...