[CALCITE-3379] Support expand STRING column expression of table during sql-to-rel conversion

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.21.0
• Fix Version/s: 1.22.0
• Component/s: core
• Labels: pull-request-available
• Assignee: Danny Chen
• Reporter: Danny Chen
• Created: 29/Sep/19 09:32
• Updated: 06/Mar/20 04:35
• Resolved: 11/Oct/19 10:59

Description

Now there are 2 ways to convert a RelOptTable to LogicalTableScan:

1. One way is to open the Config#isConvertTableAccess[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 is to use the LogicalTableScan rule, this rule would invoke RelOptTable#toRel and wrap the returned node with a LogicalTableScan.

 

The difference 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 uses InitializerContext#convertExpression to convert a SqlNode, but if the SqlNode is not validated, we always got a RexCall with SqlUnresolvedFunction. We should give the user chance to validate their SqlNode or even we can support pure string expressions which can be used to persist.

 

Another problem with #toRel is that after the expressions applied as a projection, user has no chance to apply any other relational 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

Issue Links

• links to: GitHub Pull Request #1497

Sub-Tasks

• Column expression in DDL should be validated before converting to RexNode: Closed