This join type indicates that the Index Merge optimization is used. In this case, the key column in the output row contains a list of indexes used, and key_len contains a list of the longest key parts for the indexes used. 在一个查询里面很有多索引用被用到,可能会触发index_merge的优化机...
ClickHouse是俄罗斯的Yandex于2016年开源的列式存储数据库(DBMS),使用C++语言编写,主要用于在线分析处理查询(OLAP),能够使用SQL查询实时生成分析数据报告。 OLAP(On-Line Analytical Processing)翻译为联机分析处理,专注于分析处理,从对数据库操作来看,OLAP是对数据的查询; OLTP(on-line transaction processing)翻译为联机...
Other fields in *es are * initialized here. */voidExplainPrintTriggers(ExplainState *es, QueryDesc *queryDesc){ ResultRelInfo *rInfo; bool show_relname; int numrels = queryDesc->estate->es_num_result_relations; int numrootrels = queryDesc->estate->es_num_root_result_relations; List *...
│ ExpressionList(children3)│ │ Function uniqExact(alias cnt)(children1)│ │ ExpressionList(children1)│ │ Identifier UserID │ │ Function divide(alias rpu)(children1)│ │ ExpressionList(children2)│ │ Function sum(children1)│ │ ExpressionList(children1)│ │ Identifier RequestNum │ ...
Diese Spalte enthält zum Beispiel Join-Bedingungen und Einschränkungen für WHERE-Klauseln. Beispielabfragen Sehen Sie sich die folgende EXPLAIN-Ausgabe für eine aggregierte Join-Abfrage an: explain select avg(datediff(day, listtime, saletime)) as avgwait from sales, listing where ...
aggregates– (Required) Specifies an ordered list of aggregation expressions. having– (Optional) Adds constraints to filter on groups, as implied by thehavingclause in the SPARQL query. ConditionalRouting Routes incoming solutions based on a given condition. Solutions that satisfy the condition are ...
The type column of EXPLAIN output describes how tables are joined. In JSON-formatted output, these are found as values of the access_type property. The following list describes the join types, ordered from the best type to the worst:
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The following formal has a #value! error. I havent found the reason: =SUM((($AW30:$AY30)/3)*($AZ30))/($AZ30) All cells in the formula are at zero when the stock market is closed. I have not yet tested the formula during market open because Im trying to finish before open. ...
Explain the need for cellular specialisation in a multi-cellular organism. What is the difference between chromatin and histone? List some examples of constitutive enzymes and inducible enzymes. Which mechanisms of controlling gene expression occur outside of the nucleus? Describe the structure of ...