add claude skills

skills/dbt-sql-style/SKILL.md

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+---
+name: dbt_sql_style
+description: "General SQL style guide for writing dbt models: CTE structure, formatting conventions, keywords, joins, CASE WHEN, and aggregations. Reusable across any dbt project."
+---
+
+# SQL Style Guide for dbt Models
+
+Apply these conventions to all SQL written in dbt models. Consistent style improves readability and code review speed.
+
+---
+
+## Core Rules
+
+| Rule | Convention |
+|------|-----------|
+| Keywords | **lowercase** (`select`, `from`, `where`, `join`, `group by`, `order by`) |
+| Indentation | **4 spaces** — no tabs |
+| Commas | **Trailing** (end of line), not leading |
+| One column per line | Always — no inline column lists |
+| Final SELECT | `select * from <last_cte_name>` |
+
+---
+
+## CTE Structure
+
+Always use CTEs instead of subqueries. Name each CTE after the source or concept it represents.
+
+```sql
+with source as (
+
+    select * from {{ source('system', 'table') }}
+
+),
+
+renamed as (
+
+    select
+        ----------  ids
+        id_column,
+
+        ----------  strings
+        name_column as readable_name,
+
+        ----------  dates
+        date_column as event_date,
+
+        ----------  numerics
+        amount_column as total_usd
+
+    from source
+
+)
+
+select * from renamed
+```
+
+- Blank line after the opening `(` and before the closing `)` of each CTE.
+- Blank line between each CTE block.
+
+---
+
+## Joins
+
+```sql
+from orders
+left join customers
+    on orders.customer_id = customers.id
+left join products
+    on orders.product_id = products.id
+```
+
+- **Always use `left join`** unless you have a specific reason for inner/cross.
+- Never use bare `join` — always be explicit.
+- **Always qualify columns** with table/CTE alias when joining multiple sources.
+- Place `on` conditions on the next line, indented 4 spaces.
+
+---
+
+## CASE WHEN
+
+```sql
+case
+    when status = 'cancelled' and cancelled_date is not null
+        then cancelled_date
+    when status = 'expired'
+        then expiration_date
+    else created_date
+end as effective_date,
+```
+
+- One `when` condition per line.
+- `then` indented 4 spaces under `when`.
+- Always include `else`.
+- Close with `end as <alias>`.
+
+---
+
+## Aggregations
+
+```sql
+select
+    region,
+    order_type,
+    count(*) as order_count,
+    sum(net_value) as total_net_value_usd
+
+from orders
+group by 1, 2
+```
+
+- Use **positional references** in `group by` (e.g., `group by 1, 2`).
+- Name aggregated columns clearly: `sum(x) as total_x`.
+
+---
+
+## Column Naming Conventions
+
+| Type | Pattern | Example |
+|------|---------|---------|
+| Boolean | `is_*` / `has_*` | `is_cancelled`, `has_attachment` |
+| Date | `*_date` | `created_date`, `shipped_date` |
+| Timestamp | `*_at` | `created_at`, `updated_at` |
+| Numeric amount | `*_<unit>` | `total_usd`, `quantity_ea` |
+| Foreign key | `<entity>_id` | `customer_id`, `order_id` |