Ruben Quesada Lopez created CALCITE-2959:
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Summary: 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 Quesada Lopez
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 discuss to see if / how we could find a solution to
represent this case.
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