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https://issues.apache.org/jira/browse/CALCITE-2959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17676025#comment-17676025
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Thomas Rebele commented on CALCITE-2959:
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Maybe the {{EnhancedScan}} could output the sort fields as well:
{code:java}
Sort(1,2) // can be removed, because it is already satisfied by the input
Project(0=$0, 1=$2, 2=$3) // --> Collation: [1,2]
EnhancedScan(table=Person, sort={$2.city ASC, $2.street DESC}) // outputs
name, address, tmp_address_city, tmp_address_street --> Collation: [2,3] {code}
The difficulty would be then to translate/rewrite $1.city to $2, and $1.street
to $3.
> Support collation on struct fields
> ----------------------------------
>
> Key: CALCITE-2959
> URL: https://issues.apache.org/jira/browse/CALCITE-2959
> Project: Calcite
> Issue Type: New Feature
> Reporter: Ruben Q L
> Priority: Major
>
> Currently, the class {{RelFieldCollation}} is used to define _"the ordering
> of one field of a RelNode whose output is to be sorted"_. This representation
> can hold only "simple" fields. In case of struct fields, a projection needs
> to be applied in order to reference the struct field as a simple one. For
> example, given this table:
> {code}
> CREATE TYPE Address AS (
> street VARCHAR(20) NOT NULL,
> zipcode VARCHAR(20) NOT NULL,
> city VARCHAR(20) NOT NULL);
> CREATE TABLE Person (
> id VARCHAR(20) NOT NULL,
> name VARCHAR(20) NOT NULL,
> address Address NOT NULL);
> {code}
> With a SQL query such as: "{{SELECT p.name, p.address.city FROM Person p
> ORDER BY p.address.city}}" the pseudo-plan generated would look like:
> {code}
> Sort(1) // --> Collation: [1]
> Project(0=$1, 1=$2.city)
> Scan(table=Person)
> {code}
> However, what would happen if we had a specific Scan operator that would
> guarantee us that the records would be scanned already ordered by
> address.city? Something like:
> {code}
> EnhancedScan(table=Person, sort=$2.city) // --> Collation???
> {code}
> The collation of such an operator cannot be represented with the current
> Calcite capabilities (RelFieldCollation), because it would not be a "simple"
> field, but a struct field, i.e. we would need a new collation abstraction to
> represent it, e.g. [2.city] or [2.2]
> I would like to open the discussion to see if / how we could find a solution
> to represent this case.
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