操作类型:全表扫描、索引扫描、连接操作(Hash Join/Sort Merge Join)等。 资源估算:各步骤的成本(Cost)、实际执行时间(Actual Time)。 数据流向:数据如何在节点间传输(如 Redistribute、Broadcast)。 2. GaussDB 特色优化 相较于传统数据库,GaussDB 在执行计划中增加了分布式特性标识: 数据分片策...
The following is a basic example of openCypherexplainoutput. The query is a single-node lookup in the air routes dataset for a node with the airport codeATLthat invokesexplainusing the details mode: ## sample queryaws neptune-graph execute-query \ --region <region> \ --graph-identifier <...
<derivedN>:ID值n的行的派生表结果,派生表可能是从FROM子句中的一个子查询生成的(The row refers to the derived table result for the row with an id value of N. A derived table may result, for example, from a subquery in the FROM clause.)。 <subqueryN>:ID值n的行的物化子查询结果。 4....
unionM,N: The row refers to the union of the rows with id values of M and N. derivedN: The row refers to the derived table result for the row with an id value of N. A derived table may result, for example, from a subquery in the FROM clause. subqueryN: The row refers to the...
The following example returns the query plan for the same query with verbose output: explain verboseselecteventid, eventname,event.venueid, venuenamefromevent, venuewhereevent.venueid = venue.venueid; QUERY PLAN ---{HASHJOIN:startup_cost2.52:total_cost58653620.93:plan_rows8712:plan_width43:best...
This is how many blocks you processed in "consistent read" mode. This will include counts of blocks read from the rollback segment in order to roll back a block. This is the mode you read blocks in with a SELECT, for example. Also, when you do a searched UPDATE/DELETE, you read the...
In this example only the rows from the sales tables need to be sorted (ID 5), the rows from the products table are already sorted on the join column coming from the primary key index access (ID 4). Figure 19: Example plan output using SORT MERGE JOIN Beginning with Oracle Database ...
When you specify FORMAT=JSON with EXPLAIN, the output has no single property directly equivalent to select_type; the query_block property corresponds to a given SELECT. Properties equivalent to most of the SELECT subquery types just shown are available (an example being materialized_from_subquery ...
When you specify FORMAT=JSON with EXPLAIN, the output has no single property directly equivalent to select_type; the query_block property corresponds to a given SELECT. Properties equivalent to most of the SELECT subquery types just shown are available (an example being materialized_from_subquery ...
MERGE JOIN SORT JOIN TABLE ACCESS FULL EMP [ANALYZED] SORT JOIN TABLE ACCESS FULL DEPT [ANALYZED] Sorting is an expensive operation, especially with large tables. Because of this, SMJ is often not a particularly efficient join method.