Danny Chen created CALCITE-3379:
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Summary: Support expand atom expression in table to relational
node conversion
Key: CALCITE-3379
URL: https://issues.apache.org/jira/browse/CALCITE-3379
Project: Calcite
Issue Type: Improvement
Components: core
Affects Versions: 1.21.0
Reporter: Danny Chen
Assignee: Danny Chen
Fix For: 1.22.0
Now there are 2 ways to convert a RelOptTable to LogicalTableScan:
1. One way is tp open the Config#sConvertTableAccess[1] flag and the
SqlToRelConverter would invoke the #toRel method which transforms the table to
a node returned by the user(Usually a table scan).
2. Another way it to use the LogicalTableScan rule, this rule would invoke
RelOptTable#toRel and wrap the returned node with a LogicalTableScan.
The different between 1 and 2 is that, 2 happens in the planning rule but 1
happens in sql-to-rel conversion, 1 also supports to expand the table columns
based on the defined default values expressions, see
InitializerExpressionFactory#newColumnDefaultValue.
The problem with the InitializerExpressionFactory#newColumnDefaultValue is that
it use InitializerContext#convertExpression to convert a SqlNode, if the
SqlNode is not validated, we always got a RexCall with SqlUnresolvedFunction.
We should give the user change to validate their SqlNode or even we can support
pure string expressions because they can be used to persist.
Another problem with #toRel is that after the expressions applied as a
projection, use has no change to apply any other rel nodes if they want, we can
actually support this, the same way as we support the column expressions.
[1]https://github.com/apache/calcite/blob/2dc97e6723e1b5bf762540f87ffffb5cd1a848a1/core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java#L5605
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