Is this your first time submitting a feature request?

• I have read the expectations for open source contributors
• I have searched the existing issues, and I could not find an existing issue for this feature
• I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

Describe the feature

Error if there are duplicate columns defined in the check_col configuration of a snapshot
Currently, the check strategy for Snapshots does not throw an error if there are duplicate column names specified in the check_cols config, and accidentally specifying a column twice results in a record being inserted even if none of the column values changed.

Recreation Steps (Tested on Snowflake and BigQuery)

1. Create a model for mocked data called test_staging.sql:

with

source as (
    select
        '123abc' as surrogate_key,
        '2' as id,
        'N' as status,
        coalesce(cast('2024-01-01' as date), current_date) as birth_date,
        '456 Stripe Ln' as address,
        'christine@dbtlabs.com' as email
)

select * from source

2. Create a model in the snapshots folder called dupes_issue.sql:

{% snapshot dupes_issue %}
    {{
        config(
            unique_key='id',
            strategy='check',
            check_cols=[
                'id',
                'id',
                'status',
                'address',
                'birth_date',
                'email'
            ],
            target_schema=target.schema,
            invalidate_hard_deletes=false
        )
    }}

    select * from {{ ref('test_staging') }}
 {% endsnapshot %}

3. Run the snapshot with dbt build -s +dupes_issue. Inspect the results (you should only see one record).
4. Run the snapshot again and inspect the results - you should see duplicate records:
   

Describe alternatives you've considered

This is easily fixed by removing the duplicate column, but I believe we could make the user experience better in terms of troubleshooting.

Who will this benefit?

Anyone using snapshots!

Speaking from my own experience, this came from troubleshooting a snapshot with ~135 columns in the check_col config (which was looked at many times over about two weeks by me and another team). Having an error thrown at us would have saved all of us some time.

Are you interested in contributing this feature?

No response

Anything else?

No response