Flexible delete+insert incremental strategy that purely relies on incremental_predicates

[dlord]

This allows us to perform fine-grained optimizations that does not rely on the unique key. This optimization is important for data warehouses like Redshift, where there is no concept of primary/unique keys and indexes.

resolves dbt-labs/dbt-core#10655

Problem

Full description of the problem can be found here

Solution

This PR makes the incremental_predicates mandatory if no unique_key. was supplied. Below is an example config:

{{ config(materialized="incremental",
            incremental_strategy='delete+insert',
            incremental_predicates = [
                "DBT_INTERNAL_DEST.event_time >= (select min(event_time) from DBT_INTERNAL_SOURCE)"
            ],
) }}

The DBT_INTERNAL_DEST and DBT_INTERNAL_SOURCE are translated to their equivalent table names using a simple string replace. This change affects the generated delete statement. Here is an example:

delete
from
  "source_db"."dbt"."source_table"
where
  (
    "source_db"."dbt"."source_table".event_time >= (select min(event_time) from "source_table__dbt_tmp173111887980")
  );

This change no longer allows the delete+insert strategy to be used as if it were an append strategy by omitting the unique_key.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development, and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX

[github-actions]

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