ATTACH DATABASE command in SQLite

The ATTACH DATABASE command in SQLite is used to attach one or more external databases to the current database connection. This allows you to access tables and data from multiple databases within the same SQL statements.

Here's the syntax for the `ATTACH DATABASE` command:

ATTACH DATABASE 'external_database_file' AS alias_name;

- external_database_file: The path to the external SQLite database file that you want to attach.

- alias_name: An optional alias to refer to the attached database in subsequent SQL statements. If not specified, SQLite uses the last component of the file name.

Once attached, you can refer to tables in the attached database using the alias name followed by a dot (`.`) and the table name.

Example:

ATTACH DATABASE 'other.db' AS other;

SELECT * FROM other.table_name;

Here are some key points to note about the ATTACH DATABASE command:

1. Multiple Attachments: You can attach multiple external databases to the same connection by issuing multiple `ATTACH DATABASE` commands.

2. Database Detachment: To detach an attached database, you can use the `DETACH DATABASE` command followed by the alias name.

3. Transaction Isolation: Each attached database operates within its own transactional context, but you can still perform transactions across attached databases using the appropriate SQL statements.

4. Temporary Attachments: You can attach in-memory or temporary databases using the `ATTACH DATABASE` command, allowing you to manipulate data without the need for persistent storage.

5. Error Handling: If the specified database file does not exist or cannot be opened, SQLite will raise an error, and the attachment will fail.

The ATTACH DATABASE command in SQLite provides a flexible way to work with multiple databases simultaneously, enabling various database operations and data manipulation tasks within a single SQL connection.