Add documentation for lab service requests by category for external vendors

Care/Operations/lab_service_requests_by_category_external_vendors_ssmm.md

@@ -0,0 +1,52 @@
+
+# Lab Service Requests by Category (External Vendors) - SSMM
+
+> Monthly count of lab service requests grouped by external vendor category and status
+
+## Purpose
+
+Returns the monthly count of lab `emr_servicerequest` records at SSMM, grouped by external vendor resource category and request status. Each row shows the month, vendor category, status, and the number of requests.
+
+
+## Parameters
+
+| Parameter | Type | Description | Example |
+|-----------|------|-------------|---------|
+| `service_request_status` | TEXT | Filter by service request status | `'completed'` |
+| `category` | TEXT | Filter by resource category title (exact match on `emr_resourcecategory.title`) | `'External Lab - Vendor A'` |
+| `date` | DATE / range | Metabase date filter (bound to `sr.created_date`) | `'2026-06-01'` |
+
+---
+
+## Query
+
+```sql
+SELECT
+  TO_CHAR(DATE_TRUNC('month', sr.created_date), 'YYYY-MM') AS month,
+  rc.title AS category,
+  sr.status,
+  COUNT(DISTINCT sr.id) AS total_requests
+FROM emr_servicerequest sr
+JOIN emr_activitydefinition ad 
+  ON ad.id = sr.activity_definition_id
+CROSS JOIN LATERAL unnest(ad.charge_item_definitions) AS cid_id
+JOIN emr_chargeitemdefinition cid 
+  ON cid.id = cid_id
+JOIN emr_resourcecategory rc 
+  ON rc.id = cid.category_id
+WHERE sr.deleted = FALSE
+  AND sr.category = 'laboratory'
+  AND rc.id IN (49, 50, 51, 52)
+  --[[AND sr.status = {{service_request_status}}]]
+  --[[AND rc.title = {{category}}]]
+  --[[AND {{date}}]]
+GROUP BY DATE_TRUNC('month', sr.created_date), rc.title, sr.status
+ORDER BY DATE_TRUNC('month', sr.created_date) DESC, rc.title, sr.status;
+```
+
+## Notes
+
+- `rc.id IN (49, 50, 51, 52)` is hardcoded — these correspond to the SSMM external lab vendor resource categories. Update this list if category IDs change or new vendors are added.
+- Months are formatted as `YYYY-MM` for easy grouping and sorting; results are ordered with the most recent month first.
+
+*Last updated: 2026-06-19*