Maryann Xue created CALCITE-1208:
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Summary: Improve two-level column structure handling
Key: CALCITE-1208
URL: https://issues.apache.org/jira/browse/CALCITE-1208
Project: Calcite
Issue Type: Improvement
Components: core
Affects Versions: 1.7.0
Reporter: Maryann Xue
Assignee: Maryann Xue
Calcite now has support for nested column structure in parsing and validation,
by representing the inner-level columns as a RexFieldAccess based on a
RexInputRef. Meanwhile it does not flatten the inner level structure in
wildcard expansion, which would then cause an UnsupportedOperationException in
Avatica.
The idea is to take into account this nested structure in column resolving, but
to flatten the structure when translating to RelNode/RexNode.
For example, if the table structure is defined as
{code}VARCHAR K0,
VARCHAR C1,
RecordType(INTEGER C0, INTEGER C1) F0,
RecordType(INTEGER C0, INTEGER C2) F1{code}
, it should be viewed as a flat type like
{code}VARCHAR K0,
VARCHAR C1,
INTEGER F0.C0,
INTEGER F0.C1,
INTEGER F1.C0,
INTEGER F1.C2{code}
, so that:
1) Column reference "K0" is translated as {{$0}}
2) Column reference "F0.C1" is translated as {{$3}}
3) Wildcard "*" is translated as: {{$0, $1, $2, $3, $4, $5}}
4) Complex-column wildcard "F1.*", which is translated as {{$2, $3}}
And we would like to resolve columns based on the following rules (here we only
consider the "suffix" part of the qualified names, which means the table
resolving is already done by this time):
a) A two-part column name is matched with its first-level column name and its
second-level column name. For example, "F1.C0" corresponds to $4; "F1,X" will
throw a column not found error.
b) A single-part column name is matched against non-nested columns first, and
if no matches, it is then matched against those second-level column names. For
example, "C1" will be matched as "$1" instead of "$3", since non-nested columns
have a higher priority; "C2" will be matched as "$5"; "C0" will lead to an
ambiguous column error, since it exists under both "F0" and "F1".
c) We would also like to have a way for defining "default first-level column"
so that it has a precedence in column resolving over other first-level columns.
For example, if "F0" is defined as default, "C0" will not cause an ambiguous
column error, but instead be matched as "$2".
d) Reference to first-level column only without wildcard is not allowed, e.g.,
"F1".
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