cross db queries in redshift

Describe the bug

When using source database that is different from the target (https://docs.getdbt.com/reference/resource-properties/database), I ran into an issue that adapter doesn’t fetch columns, since it seems like it looks only into target db for meta information about them: https://github.com/fishtown-analytics/dbt/blob/develop/plugins/redshift/dbt/include/redshift/macros/adapters.sql#L79

Steps To Reproduce

1. Have target db different from source db
2. Run model based on source table that doesn’t exist on target using adapter macroses

Expected behavior

Adapter expected to get meta information about source tables from source database

Screenshots and log output

Not applicable

System information

Which database are you using dbt with?

• postgres
• redshift
• bigquery
• snowflake
• other (specify: ____________)

The output of dbt --version:

0.17.2

The operating system you’re using: OSX

The output of python --version: 3.9.4

Additional context

Not applicable

[sonac]

indeed, I’d be keen helping, since this functionality would ease our testing setup.

[jtcohen6]

This was resolved by #3408 — as in, the bit we can do for now: querying sources that live in other databases when using RA3 nodes. When Redshift adds write DDL/DML support, we can consider adding support for other resources types in other databases.