docs: Add custom-query code snippet for Cloud Run sample documentation (

#1124)

samples/run/README.md

@@ -32,7 +32,7 @@ gcloud run deploy --image gcr.io/${PROJECT_ID}/data-validation \
 
 ### Test Cloud Run Endpoint
 
-You can easily run a request via Python.  For a quick test, we have provided this logic in `test.py` to run a validation against a public BigQuery table. The example is similar and also shows how you can forward results to BigQuery from the Cloud Run job:
+You can easily run a request via Python.  For a quick test, we have provided this logic in `test.py` to run a validation against a public BigQuery table. The example below is similar and also shows how you can forward results to BigQuery from the Cloud Run job:
 
 ```python
 # Copyright 2020 Google LLC
@@ -95,8 +95,7 @@ data = {
       "type": "BigQuery",
       "project_id": PROJECT_ID,
       "table_id": "pso_data_validator.results"
-   },
-
+    },
     "aggregates": [
         {
             "source_column": None,
@@ -112,6 +111,45 @@ res = requests.post(
 print(res.content.decode())
 ```
 
+If you intend to execute custom query validations, you will need to declare each aggregation column from your SQL query inside the `data` configuration object as shown in the code snippet below:
+
+```python
+query = """
+SELECT start_station_id, 
+       SUM(CASE WHEN bikeid = 18104 THEN 1 END ) AS bike_18104
+FROM `bigquery-public-data.new_york_citibike.citibike_trips`
+WHERE bikeid = 18104
+GROUP BY start_station_id
+ORDER BY bike_18104 DESC
+"""
+
+data = {
+    "source_conn": {
+        "source_type": "BigQuery",
+        "project_id": PROJECT_ID,
+    },
+    "target_conn": {
+        "source_type": "BigQuery",
+        "project_id": PROJECT_ID,
+    },
+    "type": "Custom-query",
+    "custom_query_type": "Column",
+    "schema_name": "bigquery-public-data.new_york_citibike",
+    "table_name": "citibike_stations",
+    "source_query": query,
+    "target_query": query,
+    "aggregates": [
+        {
+            "source_column": "bike_18104",
+            "target_column": "bike_18104",
+            "field_alias": "sum_bike",
+            "type": "sum",
+        }
+    ],
+}
+```
+
+
 ### Oracle Setup
 
 If you would like to use Data Validation against an Oracle DB you will need to