doc: managing multiple databases (#327)

Author: TianyuZhang1214

README.md

@@ -201,9 +201,13 @@ Looking to load Parquet files into MyDuck Server and start querying? Follow our
 
 Already have a DuckDB file? You can seamlessly bootstrap MyDuck Server with it. See our [DuckDB file bootstrapping guide](docs/tutorial/bootstrap.md) for more details.
 
+### Managing Multiple Databases
+
+Easily manage multiple databases in MyDuck Server, same as Postgres. For step-by-step instructions and detailed guidance, check out our [Database Management Guide](docs/tutorial/manage-multiple-databases.md).
+
 ### Backup and Restore with Object Storage
 
-To back up and restore your MyDuck Server database using object storage, refer to our [backup and restore guide](docs/tutorial/backup-restore.md) for detailed instructions.
+To back up and restore your databases inside MyDuck Server using object storage, refer to our [backup and restore guide](docs/tutorial/backup-restore.md) for detailed instructions.
 
 ### LLM Integration
 
@@ -217,8 +221,8 @@ MyDuck Server can be seamlessly accessed from the Python data science ecosystem.
 
 We have big plans for MyDuck Server! Here are some of the features we’re working on:
 
-- [ ] Arrow Flight SQL.
-- [ ] Multiple DB.
+- [x] Arrow Flight SQL.
+- [x] Multiple DB.
 - [ ] Authentication.
 - [ ] ...and more! We’re always looking for ways to make MyDuck Server better. If you have a feature request, please let us know by [opening an issue](https://github.com/apecloud/myduckserver/issues/new).
 

docs/tutorial/manage-multiple-databases.md

@@ -0,0 +1,40 @@
+### Managing Databases in MyDuck Server
+
+MyDuck Server offers basic database operations similar to PostgreSQL. Each database in MyDuck Server is represented as a single DuckDB data file. As a result, all database operations are mapped to corresponding file operations. Below are the key commands for managing databases in MyDuck Server:
+
+#### 1. `CREATE DATABASE`
+The `CREATE DATABASE db_name` command creates a new database by generating a file named `db_name.db`. This database is then attached to the current DuckDB client session.
+
+**Example:**
+```sql
+CREATE DATABASE my_database;
+```
+
+This will create a new database file `my_database.db` and attach it to the current session.
+
+#### 2. `DROP DATABASE`
+The `DROP DATABASE db_name` command detaches the specified database from the current session and deletes the associated database file (`db_name.db`).
+
+**Example:**
+```sql
+DROP DATABASE my_database;
+```
+
+This will detach `my_database` from the current session and permanently delete the file `my_database.db` from storage.
+
+#### 3. `USE DATABASE`
+The `USE db_name` command allows you to switch the current session to a different database. After executing this command, all subsequent operations will be performed on the specified database.
+
+**Example:**
+```sql
+USE my_database;
+```
+
+This command switches the current session to the `my_database` database, and all further queries will be executed on it.
+
+---
+
+### Important Notes
+
+- This feature is available only through the PostgreSQL protocol.
+- To backup your database to object storage or restore it from a backup file, please refer to the [Backup and Restore Guide](./backup-restore.md).