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Posted to issues@spark.apache.org by "Hyukjin Kwon (JIRA)" <ji...@apache.org> on 2019/05/21 04:34:27 UTC
[jira] [Resolved] (SPARK-14032) Eliminate Unnecessary
Distinct/Aggregate
[ https://issues.apache.org/jira/browse/SPARK-14032?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Hyukjin Kwon resolved SPARK-14032.
----------------------------------
Resolution: Incomplete
> Eliminate Unnecessary Distinct/Aggregate
> ----------------------------------------
>
> Key: SPARK-14032
> URL: https://issues.apache.org/jira/browse/SPARK-14032
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.0.0
> Reporter: Xiao Li
> Priority: Major
> Labels: bulk-closed
>
> Distinct is an expensive operation. If possible, we should avoid it. When the child operators can guarantee the distinct, we can remove it.
> For example, in the following TPC-DS query 38, the child is distinct, and thus, we can remove the top Distinct after converting Intersect to Left-semi + Distinct.
> {code}
> select count(*) from (
> select distinct c_last_name, c_first_name, d_date
> from store_sales, date_dim, customer
> where store_sales.ss_sold_date_sk = date_dim.d_date_sk
> and store_sales.ss_customer_sk = customer.c_customer_sk
> and d_month_seq between [DMS] and [DMS] + 11
> intersect
> select distinct c_last_name, c_first_name, d_date
> from catalog_sales, date_dim, customer
> where catalog_sales.cs_sold_date_sk = date_dim.d_date_sk
> and catalog_sales.cs_bill_customer_sk = customer.c_customer_sk
> and d_month_seq between [DMS] and [DMS] + 11
> intersect
> select distinct c_last_name, c_first_name, d_date
> from web_sales, date_dim, customer
> where web_sales.ws_sold_date_sk = date_dim.d_date_sk
> and web_sales.ws_bill_customer_sk = customer.c_customer_sk
> and d_month_seq between [DMS] and [DMS] + 11
> ) hot_cyst
> {code}
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