[CALCITE-4209] In RelBuilder, add an option to not simplify LIMIT 0 to an empty relation - ASF JIRA

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Details

Type: Improvement
Status: Closed
Priority: Major
Resolution: Fixed
Affects Version/s: None
Fix Version/s: 1.26.0
Component/s: None
Labels:
- pull-request-available

Description

When you call relBuilder.limit(0, 0) it triggers a call to RelBuilder.empty here.

This is fine as the default behavior, but for cases where we intend to convert the relational algebra to SQL and display it somewhere, it would be preferable to turn this behavior off, either as an extra flag to this method or a configuration parameter. The call to empty() often results in a VALUES or a select list of literal NULLs, which looks ugly and can confuse a user.

Moreover, there are certain databases (like BigQuery) that can cheaply handle a LIMIT 0 query as a form of validation, and if we munge the query with 'empty()' we lose the ability to validate its correctness by going to the DB.