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https://issues.apache.org/jira/browse/PHOENIX-4820?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16726253#comment-16726253
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Thomas D'Silva edited comment on PHOENIX-4820 at 12/20/18 10:07 PM:
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[~comnetwork] I am not very familiar with the group by/order by code, so pardon
my ignorance. I am trying to understand why the {{order by a.ak3,a.av1}} can be
optimized out. The inner query causes the rows to be ordered by {{pk2,pk3}}.
For the rows that are returned we are further doing a {{group by a.ak3,a.av1
order by a.ak3,a.av1}} which ends up grouping by {{pk3,v1}} and then ordering
by {{pk3,v1}}.
The group by will cause a single row to be returned for each {{pk3,v1}} but
that does not mean the rows will be ordered by {{pk3,v1}} right? Its not clear
to me why the order by can be optimized out.
was (Author: tdsilva):
[~comnetwork] I am not very familiar with the group by/order by code, so pardon
my ignorance. I am trying to understand why the {{ order by a.ak3,a.av1}} can
be optimized out. The inner query causes the rows to be ordered by {{pk2,pk3}}.
For the rows that are returned we are further doing a {{group by a.ak3,a.av1
order by a.ak3,a.av1}} which ends up grouping by {{pk3,v1}} and ordering by
{{pk3,v1}}.
The group by will cause a single row to be returned for each {{pk3,v1}} but
that does not mean the rows will be order by {{pk3,v1}} right? Its not clear to
me why the order by can be optimized out?
> Optimize OrderBy for ClientAggregatePlan
> ----------------------------------------
>
> Key: PHOENIX-4820
> URL: https://issues.apache.org/jira/browse/PHOENIX-4820
> Project: Phoenix
> Issue Type: Improvement
> Affects Versions: 4.14.0
> Reporter: chenglei
> Assignee: chenglei
> Priority: Major
> Fix For: 4.15.0
>
> Attachments: PHOENIX-4820-4.x-HBase-1.3.patch
>
>
> Given a table
> {code}
> create table test (
> pk1 varchar not null ,
> pk2 varchar not null,
> pk3 varchar not null,
> v1 varchar,
> v2 varchar,
> CONSTRAINT TEST_PK PRIMARY KEY (
> pk1,
> pk2,
> pk3 ))
> {code}
> for following sql :
> {code}
> select a.ak3
> from (select substr(pk1,1,1) ak1,substr(pk2,1,1) ak2,substr(pk3,1,1)
> ak3,substr(v1,1,1) av1,substr(v2,1,1) av2 from test order by pk2,pk3 limit
> 10) a group by a.ak3,a.av1 order by a.ak3,a.av1
> {code}
> Intuitively, the above OrderBy statement {{order by a.ak3,a.av1}} should be
> compiled out because it match the group by statement, but in fact it is not.
> The problem is caused by the {{QueryCompiler.compileSingleQuery}} and
> {{QueryCompiler.compileSingleFlatQuery}},for
> {{QueryCompiler.compileSingleQuery}} method,because the inner query has order
> by, so in line 520, local variable {{isInRowKeyOrder}} is false:
> {code}
> 519 context.setCurrentTable(tableRef);
> 520 boolean isInRowKeyOrder = innerPlan.getGroupBy() ==
> GroupBy.EMPTY_GROUP_BY && innerPlan.getOrderBy() == OrderBy.EMPTY_ORDER_BY;
> {code}
> In {{QueryCompiler.compileSingleFlatQuery}},when {{OrderByCompiler.compile}}
> method is invoked, the last parameter {{isInRowKeyOrder}} is false:
> {code}
> 562 OrderBy orderBy = OrderByCompiler.compile(context, select,
> groupBy, limit, offset, projector,
> 563 groupBy == GroupBy.EMPTY_GROUP_BY ?
> innerPlanTupleProjector : null, isInRowKeyOrder);
> {code}
> So in following line 156 for {{OrderByCompiler.compile}},even though the
> {{tracker.isOrderPreserving}} is true, the OrderBy statement could not be
> compiled out.
> {code}
> 156 if (isInRowKeyOrder && tracker.isOrderPreserving()) {
> {code}
> In my opinion, with GroupBy, in following line 563 for
> {{QueryCompiler.compileSingleFlatQuery}} method, when we call
> {{OrderByCompiler.compile}} method, we no need to conside the
> {{isInRowKeyOrder}}, just like the previous parameter {{tupleProjector}}
> does.
> {code}
> 562 OrderBy orderBy = OrderByCompiler.compile(context, select,
> groupBy, limit, offset, projector,
> 563 groupBy == GroupBy.EMPTY_GROUP_BY ?
> innerPlanTupleProjector : null, isInRowKeyOrder);
> {code}
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