[Bug] Fact table creation incorrectly requires all datasource identifiers

Summary

When creating a fact table, GrowthBook requires columns for every identifier defined on the datasource, even when the SQL returns a valid subset.

Replication steps

1. Configure a Databricks datasource with multiple identifier types (11 in this case).
2. Create a new fact table.
3. Edit the generated starter SQL to return timestamp and only three identifiers.
4. Save the fact table.

Expected Behavior

The fact table should save when the SQL returns timestamp and at least one valid datasource identifier. It should only fail when no valid identifiers are present.

Current Behavior

The save fails because GrowthBook requires columns for the other eight identifiers.

The user must temporarily return placeholder values for all unused identifiers, create the fact table, and then edit the SQL to remove them.