betodealmeida opened a new pull request, #38889: URL: https://github.com/apache/superset/pull/38889
<!--- Please write the PR title following the conventions at https://www.conventionalcommits.org/en/v1.0.0/ Example: fix(dashboard): load charts correctly --> ### SUMMARY <!--- Describe the change below, including rationale and design decisions --> When using an adhoc expression `$expr` for the base axis, Superset will run this query to inspect the `cursor.description` to get the result type: ```sql SELECT $expr FROM $table LIMIT 1; ``` One problem with this approach is that in some databases (ClickHouse, BigQuery, eg) this query still scans **all** rows, since it has no predicate.e for BigQuery as well. This PR changes the query to this shape: ```sql SELECT $expr FROM $table WHERE FALSE; ``` I tested the fix against 17 different databases, and for 14 of them the type was still present in the `cursor.description` even though no rows were returned: - DuckDB - SQLite - PostgreSQL - CockroachDB - MariaDB - MySQL - SQL Server - Trino - Snowflake - Databricks - Oracle - Redshift - ClickHouse - BigQuery Unfortunately I already knew that the fix wouldn't work for these databases (since I wrote the DB API 2.0 library for them): - Druid - Pinot - Shillelagh/GSheets The first two require at least one row of data to populate the `cursor.description`, since the types are inferred from the returned Python types. Shillelagh and GSheets have their own quirks due to the fact that SQLite has no proper types implementation. `¯\_(ツ)_/¯` Because of Druid and Pinot I added a new DB engine spec attribute `type_probe_needs_row`: - False: use `WHERE FALSE` - True: use `LIMIT 1` ### BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF <!--- Skip this if not applicable --> ### TESTING INSTRUCTIONS <!--- Required! What steps can be taken to manually verify the changes? --> ### ADDITIONAL INFORMATION <!--- Check any relevant boxes with "x" --> <!--- HINT: Include "Fixes #nnn" if you are fixing an existing issue --> - [ ] Has associated issue: - [ ] Required feature flags: - [ ] Changes UI - [ ] Includes DB Migration (follow approval process in [SIP-59](https://github.com/apache/superset/issues/13351)) - [ ] Migration is atomic, supports rollback & is backwards-compatible - [ ] Confirm DB migration upgrade and downgrade tested - [ ] Runtime estimates and downtime expectations provided - [ ] Introduces new feature or API - [ ] Removes existing feature or API -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
