[CT-2429] dbt show: option to use already-materialized model instead of rerunning SQL

[jtcohen6]

As a dbt developer, especially on BigQuery, I want to preview my just-built table in the fastest & cheapest way possible.

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When users run dbt show --select my_model, rather than recompiling and executing that model's SQL, give users the option to preview the already-materialized version of my_model in the data warehouse.

This goes beyond just --inline "select * from {{ ref('that_model') }}, because it would also unlock adapter-specific optimizations.

• On all data platforms, this saves compute
• On BigQuery, this saves $$$.

Options:

• Config, --from-materialized (I hate this name)
• Different command: dbt head, to match bq head?

In the short term, it would be the responsibility of users to track logical/applied state, and do their own "cache invalidation" if they've edited the model's definition since they last built it. (In the longer term, we could get cleverer about this in stateful runtime environments.)

This would be functionally identical for views and ephemeral models.

[b-per]

Throwing other options for the config name:

• --existing
• --last-refreshed
• --materialized
• --last-materialized

[jtcohen6]

In theory, this would also work for Python models — build first, then preview.

Another option is to have this command/config implicitly materialize the model first: run it, then show it. I'd rather the building be explicit, though — and then provide the option of showing the just-built thing.

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[b-per]

I'd love for this to happen! This could be very useful to save costs when querying data and avoid having people to go to their Data Warehouse interface to do so.