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

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.26.0
• Labels: pull-request-available
• Assignee: Julian Hyde
• Reporter: Steven Talbot
• Created: 01/Sep/20 16:27
• Updated: 06/Oct/20 17:16
• Resolved: 21/Sep/20 22:46

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.

Issue Links

• links to: GitHub Pull Request #2159