sql-execution-plan

问题 So I'm (still) going through some slow legacy sql views used to do calculate some averages and standarddeviations on a (sometimes) large set of data. What I end up with are views joining views joining views etc. So I though I would review the execution plan for my query. And it immediately suggested a missing index, which I then implemented. But it's still unbearably slow (so slow it times out the VB6 app querying it for data ;) ) So upon studying the execution plan further, I see that what

问题 I have the fowlloing query select * from mapping_channel_fqdn_virtual_host where id in (1, 2, 3, 4, 5, 6, 7, 8, 9, 10); explaining the above query gives me the following result: explain select * from mapping_channel_fqdn_virtual_host where id in (1, 2, 3, 4, 5, 6, 7, 8, 9, 10); +----+-------------+-----------------------------------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys |

问题 I'm not sure sure how to interpret this, but all the queries I run in sql server 2005 have a "query cost (relative to batch)" of 100%. Is there any way to reduce the cost? 回答1: If your batch (what you are executing within a given call) has one query then relative to that batch that query takes up 100% as it is the only query within that batch. I.e.: BEGIN SELECT * FROM table -- Will be 100% of batch END BEGIN SELECT * FROM table -- Will be 50% of batch SELECT * FROM table -- Will be 50% of

问题 I'm learning how to read the actual execution plan in SQL Server. I have noticed that SQL Server tends to represent intermediate value used in the physical query plan as e.g. expr1006 , expr1007 etc. (i.e. expr followed by a number). Here is a screenshot. Notice near the bottom, the expressions expr1006, expr1008, expr1009 listed in the section output list . It it possible to find out what they really represent? 回答1: Right click the compute scalar and choose "properties". Look in the "Defined

问题 I'm learning how to read the actual execution plan in SQL Server. I have noticed that SQL Server tends to represent intermediate value used in the physical query plan as e.g. expr1006 , expr1007 etc. (i.e. expr followed by a number). Here is a screenshot. Notice near the bottom, the expressions expr1006, expr1008, expr1009 listed in the section output list . It it possible to find out what they really represent? 回答1: Right click the compute scalar and choose "properties". Look in the "Defined

问题 This line of code converts a dataFrame to a logical plan val logical = df.queryExecution.logical Can we do the opposite, meaning extracting from the logical plan, the dataframes used ? 回答1: in Dataset object there is a method: def ofRows(sparkSession: SparkSession, logicalPlan: LogicalPlan) so if you have a logical plan, you can transform it into a DataFrame by calling Dataset.ofRows(sparkSession, logical) 来源： https://stackoverflow.com/questions/43763246/spark-extract-dataframe-from-logical

问题 This line of code converts a dataFrame to a logical plan val logical = df.queryExecution.logical Can we do the opposite, meaning extracting from the logical plan, the dataframes used ? 回答1: in Dataset object there is a method: def ofRows(sparkSession: SparkSession, logicalPlan: LogicalPlan) so if you have a logical plan, you can transform it into a DataFrame by calling Dataset.ofRows(sparkSession, logical) 来源： https://stackoverflow.com/questions/43763246/spark-extract-dataframe-from-logical

来源： https://stackoverflow.com/questions/64542167/included-columns-are-used-in-seek-operator

来源： https://stackoverflow.com/questions/64542167/included-columns-are-used-in-seek-operator

问题 Is there any proper resource from where we can understand explain plan generated by hive completely? I have tried searching it in the wiki but could not find a complete guide to understand it. Here is the wiki which briefly explains how explain plan works. But I need further information on how to infer the explain plan. https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Explain 回答1: I will try to explain a litte what I know. The execution plan is a description of the tasks