diff --git a/docs/practices.md b/docs/practices.md
index f9aba97..e59cbc2 100644
--- a/docs/practices.md
+++ b/docs/practices.md
@@ -11,10 +11,30 @@ SQL practices
 
 - Count the number of subordinate 'ENTERPRISE\_CUSTOMER' organizations for each organization.
 
+```sql
+SELECT
+    COUNT(customers.*) AS "subordinates_count",
+    organizations.id AS "id"
+FROM organizations
+LEFT OUTER JOIN enterprise_sales_enterprise_customers customers ON customers.sales_organization_id = organizations.id
+GROUP BY organizations.id
+ORDER BY organizations.id ASC
+;
+```
+
 # Practice 2
 
 - Calculate the center of each `japan_segment`.
 
+```sql
+SELECT
+    id,
+    ST_X(ST_Centroid(bounds)) AS "longitude",
+    ST_Y(ST_Centroid(bounds)) AS "latitude"
+FROM japan_segments
+;
+```
+
 # Practice 3
 
 - Select `japan_segments` within the bounds represented as the following GeoJSON.
diff --git a/test/test_example.py b/test/test_example.py
index 3904377..8a74cef 100644
--- a/test/test_example.py
+++ b/test/test_example.py
@@ -95,7 +95,14 @@ class TestExample(DbTest):
             os.path.join(PATH_TO_SQL_DIR, "japan_segments.sql")
         )
 
+        # PostGIS is very useful!
         sql = """
+        SELECT
+            id,
+            ST_X(ST_Centroid(bounds)) AS "longitude",
+            ST_Y(ST_Centroid(bounds)) AS "latitude"
+        FROM japan_segments
+        ;
         """
         with conn.cursor(cursor_factory=RealDictCursor) as cur:
             cur.execute(sql)