add claude skills

skills/dbt-create-mart/SKILL.md

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+---
+name: dbt_create_mart
+description: "Step-by-step instructions for creating dbt Mart models (facts and dimensions) as thin wrappers over transform models. Use for any dbt + Snowflake project."
+---
+
+# Create a dbt Mart Model (Fact or Dimension)
+
+Mart models are **thin wrappers** over transform models. They expose clean, BI-ready tables without duplicating business logic.
+
+---
+
+## Fact Model Steps
+
+**1. Name the file**
+- Pattern: `fct_<domain>_<metric>.sql`
+- Example: `fct_sales_orders.sql`, `fct_ar_open_items.sql`
+- Lives in `models/marts/facts/`
+
+**2. Write a thin SELECT wrapper**
+
+Option A — expose all columns (most common):
+```sql
+select {{ dbt_utils.star(ref('<trf_model_name>')) }}
+from {{ ref('<trf_model_name>') }}
+```
+
+Option B — add a light filter or derived column:
+```sql
+select
+    *,
+    <derived_column> as <alias>
+from {{ ref('<trf_model_name>') }}
+where <filter_condition>
+```
+
+**3. Materialization**
+- Default: `view` (inherited from `dbt_project.yml`).
+- Override to `table` only if the BI tool performs poorly on views.
+
+---
+
+## Dimension Model Steps
+
+**1. Name the file**
+- Pattern: `dim_<entity>.sql`
+- Example: `dim_customers.sql`, `dim_materials.sql`
+- Lives in `models/marts/dim/`
+
+**2. Write the SELECT**
+- Dimensions are usually deduped/distinct entity lists from staging or transform.
+```sql
+select distinct
+    <natural_key>          as <entity>_key,
+    <descriptive_field_1>,
+    <descriptive_field_2>
+from {{ ref('<stg_or_trf_model>') }}
+where <natural_key> is not null
+```
+
+**3. Add schema entry**
+- File: `models/marts/schema.yml`
+- Every fact: test `unique` + `not_null` on the primary key.
+- Every dimension: test `unique` + `not_null` on the surrogate/natural key.
+- Add `relationships` tests on foreign keys in fact models.
+
+---
+
+## Rules
+
+| Rule | Detail |
+|------|--------|
+| No business logic | Mart = wrapper only; logic belongs in transform |
+| Materialization | `view` by default; `table` only if needed for BI performance |
+| Column naming | `snake_case` for marts; inherit from the transform model |
+| `ref()` only | Always reference the transform model with `{{ ref() }}` |
+| BI-facing names | Rename columns here if the BI layer needs friendlier names |
+
+---
+
+## Templates
+
+See `mart_fct_template.sql` and `mart_dim_template.sql` in this folder.