workspace/skills/dbt-create-transform/SKILL.md

name, description

name	description
dbt_create_transform	Step-by-step instructions for creating a dbt incremental transform model with business logic, joins, and date filters. Use for any dbt + Snowflake project.

Create a dbt Transform Model

Transform models contain business logic — joins, aggregations, date filters, and derived columns. They are almost always incremental to handle large datasets efficiently.

---

Steps

1. Name the file

• Pattern: trf_<domain>_<entity>.sql
• Examples: trf_sales_orders.sql, trf_ar_open_items.sql
• Lives in models/transform/<domain>/

2. Add the config block (top of file)

{{ config(
    materialized = 'incremental',
    unique_key = ['key_col_1', 'key_col_2'],
    on_schema_change = 'sync_all_columns',
    incremental_strategy = 'delete+insert'
) }}

• unique_key: list of columns that uniquely identify a row.
• on_schema_change = 'sync_all_columns': automatically adds/removes columns on model changes.

3. (Optional) Add full-refresh protection

{{ sie_dbt_utils.full_refresh_protection() }}

Prevents accidental full-refresh data loss in production. Add on line 1 if using sie_dbt_utils.

4. Define CTEs — one per source model

• Name each CTE after the staging model or business concept it represents.
• Apply tenant/client filters immediately in the CTE (e.g., WHERE mandt IN ('022', '100')).

with
orders as (
    select * from {{ ref('stg_<system>_<table>') }}
    where mandt in ('022', '100')   -- replace with your tenant filter
),
customers as (
    select * from {{ ref('stg_<system>_kna1') }}
),

5. Write the final SELECT with joins

• Use UPPER_CASE for column aliases in transform models (SAP/warehouse convention).
• Qualify all columns with CTE alias when joining.
• Use left join; never bare join.

6. Add date range filter

• Filter to a rolling window (e.g., last 2 fiscal years) to keep the table small.
• Siemens fiscal year = calendar year + 3 months shift:

  where year(dateadd(month, 3, to_date(erdat, 'yyyymmdd')))
        >= year(dateadd(year, -2, dateadd(month, 3, getdate())))
  

  Adapt the date logic to your project's fiscal/calendar year convention.

7. Add the incremental block

{% if is_incremental() %}
    and <date_column> >= (select max(<date_column>) from {{ this }})
{% endif %}

Prefer sie_dbt_utils.incremental_filter('col') if available — it compiles the MAX watermark at build time.

8. Add schema entry

• File: models/transform/<domain>/schema.yml
• Include model description and unique + not_null on the primary key.

---

Rules

Rule	Detail
Materialization	incremental (set in config block)
Column casing	UPPER_CASE aliases for transform/distribute layers
Tenant filter	Apply mandt/client filter in each base CTE
No hardcoding	Use {{ ref() }} and {{ source() }} only
Incremental strategy	delete+insert with unique_key

---

Template

See trf_template.sql in this folder.