Introducing query JSON and foreign keys in Query databases chapter.

Author: Oxyjun

src/content/docs/d1/best-practices/query-d1.mdx

@@ -12,6 +12,10 @@ There are a number of ways you can interact with a D1 database:
 3. Using [D1 REST API](/api/operations/cloudflare-d1-create-database).
 4. Using [D1 Wrangler commands](/d1/wrangler-commands/).
 
+:::note
+D1 is compatible with most SQLite's SQL convention since it leverages SQLite's query engine.
+:::
+
 ## Query D1 with Workers Binding API
 
 Workers Binding API primarily interacts with the data plane, and allows you to query your D1 database from your Worker.
@@ -47,29 +51,55 @@ Refer to [Workers Binding API](/d1/worker-api/) for more information.
 
 ## Query D1 with SQL API
 
-D1 is compatible with most SQLite's SQL convention since it leverages SQLite's query engine.
+D1 understands SQLite semantics, which allows you to query a database using SQL statements via Workers BindingAPI or REST API (including Wrangler commands). Refer to [D1 SQL API](/d1/sql-api/sql-statements/) to learn more about supported SQL statements.
 
-```sh
-npx wrangler d1 execute prod-d1-tutorial --local --command="SELECT * FROM Customers"
+### Use foreign key relationships
+
+When using SQL with D1, you may wish to define and and enforce foreign key constraints across tables in a database. Foreign key constraints allow you to enforce relationships across tables, or prevent you from deleting rows that reference rows in other tables. An example of a foreign key relationship is shown below.
+
+```sql
+CREATE TABLE users (
+    user_id INTEGER PRIMARY KEY,
+    email_address TEXT,
+    name TEXT,
+    metadata TEXT
+)
+
+CREATE TABLE orders (
+    order_id INTEGER PRIMARY KEY,
+    status INTEGER,
+    item_desc TEXT,
+    shipped_date INTEGER,
+    user_who_ordered INTEGER,
+    FOREIGN KEY(user_who_ordered) REFERENCES users(user_id)
+)
 ```
 
-```sh output
-🌀 Mapping SQL input into an array of statements
-🌀 Executing on local database production-db-backend (database-id) from .wrangler/state/v3/d1:
-┌────────────┬─────────────────────┬───────────────────┐
-│ CustomerId │ CompanyName         │ ContactName       │
-├────────────┼─────────────────────┼───────────────────┤
-│ 1          │ Alfreds Futterkiste │ Maria Anders      │
-├────────────┼─────────────────────┼───────────────────┤
-│ 4          │ Around the Horn     │ Thomas Hardy      │
-├────────────┼─────────────────────┼───────────────────┤
-│ 11         │ Bs Beverages        │ Victoria Ashworth │
-├────────────┼─────────────────────┼───────────────────┤
-│ 13         │ Bs Beverages        │ Random Name       │
-└────────────┴─────────────────────┴───────────────────┘
+Refer to [Define foreign keys](/d1/sql-api/foreign-keys/) for more information.
+
+### Query JSON
+
+D1 allows you to query and parse JSON data stored within a database. For example, you can extract a value inside a JSON object.
+
+Given the following JSON object (`type:blob`) in a column named `sensor_reading`, you can extract values from it directly.
+
+```json
+{
+    "measurement": {
+        "temp_f": "77.4",
+        "aqi": [21, 42, 58],
+        "o3": [18, 500],
+        "wind_mph": "13",
+        "location": "US-NY"
+    }
+}
+```
+```sql
+-- Extract the temperature value
+SELECT json_extract(sensor_reading, '$.measurement.temp_f')-- returns "77.4" as TEXT
 ```
 
-Refer to [D1 SQL API](/d1/sql-api/sql-statements/) to learn more about supported SQL queries.
+Refer to [Query JSON](/d1/sql-api/query-json/) to learn more about querying JSON objects.
 
 ## Query D1 with REST API