[转]Oracle执行计划（ExplainPlan）说明 [转]Oracle执⾏计划（ExplainPlan）说明 原⽂地址:http://langgufu.iteye.com/blog/2158163 如果要分析某条SQL的性能问题，通常我们要先看SQL的执⾏计划，看看SQL的每⼀步执⾏是否存在问题。如果⼀条SQL平时执⾏的好好的，却有⼀天突然性能很差，如果排除了...
17K Learn to define what injection, surjective and bijective functions are. Discover the cardinality of injective, surjective and bijective functions. See examples. Related to this QuestionDescribe four ways of representing a function. Provide examples. When are two functions equal? Explain with ...
The following example returns the query plan for a CREATE TABLE AS (CTAS) statement: explain create table venue_nonulls as select * from venue where venueseats is not null; QUERY PLAN --- XN Seq Scan on venue (cost=0.00..2.02 rows=187 width=45) Filter: (venueseats IS NOT NULL) (2...
Cardinality的值对于CBO做出正确的执行计划来说至关重要。如果CBO获得的Cardinality值不够准确(通常是没有做分析或者分析数据过旧造成),在执行计划成本计算上就会出现偏差,从而导致CBO错误的制定出执行计划。 在多表关联查询或者SQL中有子查询时,每个关联表或子查询的Cardinality的值对主查询的影响都非常大,甚至可以说,C...
SELECT cardinality "Rows",lpad(' ',level-1)||operation||' '||options||' '||object_name "Plan"FROM PLAN_TABLECONNECT BY prior id = parent_idAND prior statement_id = statement_idSTART WITH id = 0AND statement_id = 'bad1'ORDER BY id;Rows Plan--- ---SELECT STATEMENTTABLE ACCESS FU...
Remove impossible constant sub expressions. For exampleWHERE '(a=1 and a=2) OR b=1'becomes'b=1'. Replace columns with other columns that has identical values: Example:WHEREa=banda=cmay be treated as'WHERE a=b and a=c and b=c'. ...
-output_rowsis the output (node) cardinality and shows the number of output rows. <location>: The nodes or distributions where the operation will occur. Options are: "Control", "ComputeNode", "AllComputeNodes", "AllDistributions", "SubsetDistributions", "Distribution", and "SubsetNodes". ...
Rows: 当前操作的Cardinality,Oracle估计当前操作的返回结果集。 Cost(CPU):Oracle 计算出来的一个数值(代价),用于说明SQL执行的代价。 Time:Oracle 估计当前操作的时间。 在看执行计划的时候,除了看执行计划本身,还需要看谓词和统计信息。 通过整体信息来判断SQL效率。
cardinalityAnnotate each subplan with a symbolic estimate of its cardinality. join implementationsRender details about theimplementation strategy of optimized MIRJoinnodes. keysAnnotate each subplan with its unique keys. node identifiersAnnotate each subplan in aPHYSICAL PLANwith its node ID. ...
('||OPTIONS||')'"Operation",OBJECT_NAME"Object", OPTIMIZER "Optimizer", COST "Cost", CARDINALITY "Cardinality", BYTES "Bytes", PARTITION_START "Partition Start", PARTITION_ID "Partition ID" , ACCESS_PREDICATES "Access Predicates", FILTER_PREDICATES "Filter Predicates"FROMPLAN_TABLE STARTWITHID...