add claude skills

skills/dbt-create-transform/SKILL.md

@@ -0,0 +1,94 @@
+---
+name: dbt_create_transform
+description: "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)**
+```sql
+{{ 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**
+```sql
+{{ 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')`).
+
+```sql
+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:
+  ```sql
+  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**
+```sql
+{% 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.