Jussi Saurio 9c87b20cb2 Merge 'Where clause subquery support' from Jussi Saurio
Closes #1282
# Support for WHERE clause subqueries
This PR implements support for subqueries that appear in the WHERE
clause of SELECT statements.
## What are those lol
1. **EXISTS subqueries**: `WHERE EXISTS (SELECT ...)`
2. **Row value subqueries**: `WHERE x = (SELECT ...)` or `WHERE (x, y) =
(SELECT ...)`. The latter are not yet supported - only the single-column
("scalar subquery") case is.
3. **IN subqueries**: `WHERE x IN (SELECT ...)` or `WHERE (x, y) IN
(SELECT ...)`
## Correlated vs Uncorrelated Subqueries
- **Uncorrelated subqueries** reference only their own tables and can be
evaluated once.
- **Correlated subqueries** reference columns from the outer query
(e.g., `WHERE EXISTS (SELECT * FROM t2 WHERE t2.id = t1.id)`) and must
be re-evaluated for each row of the outer query
## Implementation
### Planning
During query planning, the WHERE clause is walked to find subquery
expressions (`Expr::Exists`, `Expr::Subquery`, `Expr::InSelect`). Each
subquery is:
1. Assigned a unique internal ID
2. Compiled into its own `SelectPlan` with outer query tables provided
as available references
3. Replaced in the AST with an `Expr::SubqueryResult` node that
references the subquery with its internal ID
4. Stored in a `Vec<NonFromClauseSubquery>` on the `SelectPlan`
For IN subqueries, an ephemeral index is created to store the subquery
results; for other kinds, the results are stored in register(s).
### Translation
Before emitting bytecode, we need to determine when each subquery should
be evaluated:
- **Uncorrelated**: Evaluated once before opening any table cursors
- **Correlated**: Evaluated at the appropriate nested loop depth after
all referenced outer tables are in scope
This is calculated by examining which outer query tables the subquery
references and finding the right-most (innermost) loop that opens those
tables - using similar mechanisms that we use for figuring out when to
evaluate other `WhereTerm`s too.
### Code Generation
- **EXISTS**: Sets a register to 1 if any row is produced, 0 otherwise.
Has new `QueryDestination::ExistsSubqueryResult` variant.
- **IN**: Results stored in an ephemeral index and the index is probed.
- **RowValue**: Results stored in a range of registers. Has new
`QueryDestination::RowValueSubqueryResult` variant.
## Annoying details
### Which cursor to read from in a subquery?
Sometimes a query will use a covering index, i.e. skip opening the table
cursor at all if the index contains All The Needed Stuff.
Correlated subqueries reading columns from outer tables is a bit
problematic in this regard: with our current translation code, the
subquery doesn't know whether the outer query opened a table cursor,
index cursor, or both. So, for now, we try to find a table cursor first,
then fall back to finding any index cursor for that table.

Reviewed-by: Preston Thorpe <preston@turso.tech>

Closes #3847
2025-10-28 06:36:55 +02:00
2025-08-08 15:45:05 +04:00
2025-10-27 07:09:02 +02:00
2025-09-27 14:13:45 -04:00
2025-10-06 18:19:22 +04:00
2025-09-26 15:20:27 +07:00
2025-09-24 18:06:55 -03:00
2025-03-29 14:46:11 +02:00
2025-10-20 23:48:19 -05:00
2025-10-06 11:07:06 -03:00
2025-10-27 16:10:49 +02:00
2025-01-14 18:37:26 +02:00
2025-04-15 12:45:46 -03:00
2025-10-22 13:42:52 +03:00
2025-10-03 12:20:20 +03:00
2025-07-30 11:45:24 +02:00
2025-07-17 20:25:40 -03:00
2024-07-12 13:07:34 -07:00
2024-07-12 12:38:56 -07:00
2025-10-08 09:20:44 +03:00

Turso Database

Turso Database

An in-process SQL database, compatible with SQLite.

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Chat with other users of Turso (and Turso Cloud) on Discord


About

Turso Database is an in-process SQL database written in Rust, compatible with SQLite.

⚠️ Warning: This software is in BETA. It may still contain bugs and unexpected behavior. Use caution with production data and ensure you have backups.

Features and Roadmap

  • SQLite compatibility for SQL dialect, file formats, and the C API [see document for details]
  • Change data capture (CDC) for real-time tracking of database changes.
  • Multi-language support for
  • Asynchronous I/O support on Linux with io_uring
  • Cross-platform support for Linux, macOS, Windows and browsers (through WebAssembly)
  • Vector support support including exact search and vector manipulation
  • Improved schema management including extended ALTER support and faster schema changes.

The database has the following experimental features:

  • BEGIN CONCURRENT for improved write throughput using multi-version concurrency control (MVCC).
  • Encryption at rest for protecting the data locally.
  • Incremental computation using DBSP for incremental view mainatenance and query subscriptions.

The following features are on our current roadmap:

Getting Started

Please see the Turso Database Manual for more information.

💻 Command Line
You can install the latest `turso` release with:
curl --proto '=https' --tlsv1.2 -LsSf \
  https://github.com/tursodatabase/turso/releases/latest/download/turso_cli-installer.sh | sh

Then launch the interactive shell:

$ tursodb

This will start the Turso interactive shell where you can execute SQL statements:

Turso
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database
turso> CREATE TABLE users (id INT, username TEXT);
turso> INSERT INTO users VALUES (1, 'alice');
turso> INSERT INTO users VALUES (2, 'bob');
turso> SELECT * FROM users;
1|alice
2|bob

You can also build and run the latest development version with:

cargo run

If you like docker, we got you covered. Simply run this in the root folder:

make docker-cli-build && \
make docker-cli-run
🦀 Rust
cargo add turso

Example usage:

let db = Builder::new_local("sqlite.db").build().await?;
let conn = db.connect()?;

let res = conn.query("SELECT * FROM users", ()).await?;
JavaScript
npm i @tursodatabase/database

Example usage:

import { connect } from '@tursodatabase/database';

const db = await connect('sqlite.db');
const stmt = db.prepare('SELECT * FROM users');
const users = stmt.all();
console.log(users);
🐍 Python
uv pip install pyturso

Example usage:

import turso

con = turso.connect("sqlite.db")
cur = con.cursor()
res = cur.execute("SELECT * FROM users")
print(res.fetchone())
🦫 Go
go get github.com/tursodatabase/turso-go
go install github.com/tursodatabase/turso-go

Example usage:

import (
    "database/sql"
    _ "github.com/tursodatabase/turso-go"
)

conn, _ = sql.Open("turso", "sqlite.db")
defer conn.Close()

stmt, _ := conn.Prepare("select * from users")
defer stmt.Close()

rows, _ = stmt.Query()
for rows.Next() {
    var id int
    var username string
    _ := rows.Scan(&id, &username)
    fmt.Printf("User: ID: %d, Username: %s\n", id, username)
}
Java

We integrated Turso Database into JDBC. For detailed instructions on how to use Turso Database with java, please refer to the README.md under bindings/java.

🤖 MCP Server Mode

The Turso CLI includes a built-in Model Context Protocol (MCP) server that allows AI assistants to interact with your databases.

Start the MCP server with:

tursodb your_database.db --mcp

Configuration

Add Turso to your MCP client configuration:

{
  "mcpServers": {
    "turso": {
      "command": "/path/to/.turso/tursodb",
      "args": ["/path/to/your/database.db", "--mcp"]
    }
  }
}

Available Tools

The MCP server provides nine tools for database interaction:

  1. open_database - Open a new database
  2. current_database - Describe the current database
  3. list_tables - List all tables in the database
  4. describe_table - Describe the structure of a specific table
  5. execute_query - Execute read-only SELECT queries
  6. insert_data - Insert new data into tables
  7. update_data - Update existing data in tables
  8. delete_data - Delete data from tables
  9. schema_change - Execute schema modification statements (CREATE TABLE, ALTER TABLE, DROP TABLE)

Once connected, you can ask your AI assistant:

  • "Show me all tables in the database"
  • "What's the schema for the users table?"
  • "Find all posts with more than 100 upvotes"
  • "Insert a new user with name 'Alice' and email 'alice@example.com'"

MCP Clients

Claude Code

If you're using Claude Code, you can easily connect to your Turso MCP server using the built-in MCP management commands:

Quick Setup

  1. Add the MCP server to Claude Code:

    claude mcp add my-database -- tursodb ./path/to/your/database.db --mcp
    
  2. Restart Claude Code to activate the connection

  3. Start querying your database through natural language!

Command Breakdown

claude mcp add my-database -- tursodb ./path/to/your/database.db --mcp
#              ↑            ↑       ↑                           ↑
#              |            |       |                           |
#              Name         |       Database path               MCP flag
#                          Separator
  • my-database - Choose any name for your MCP server
  • -- - Required separator between Claude options and your command
  • tursodb - The Turso database CLI
  • ./path/to/your/database.db - Path to your SQLite database file
  • --mcp - Enables MCP server mode

Example Usage

# For a local project database
cd /your/project
claude mcp add my-project-db -- tursodb ./data/app.db --mcp

# For an absolute path
claude mcp add analytics-db -- tursodb /Users/you/databases/analytics.db --mcp

# For a specific project (local scope)
claude mcp add project-db --local -- tursodb ./database.db --mcp

Managing MCP Servers

# List all configured MCP servers
claude mcp list

# Get details about a specific server
claude mcp get my-database

# Remove an MCP server
claude mcp remove my-database
Claude Desktop

For Claude Desktop, add the configuration to your claude_desktop_config.json file:

{
  "mcpServers": {
    "turso": {
      "command": "/path/to/.turso/tursodb",
      "args": ["./path/to/your/database.db.db", "--mcp"]
    }
  }
}
Cursor

For Cursor, configure MCP in your settings:

  1. Open Cursor settings
  2. Navigate to Extensions → MCP
  3. Add a new server with:
    • Name: turso
    • Command: /path/to/.turso/tursodb
    • Args: ["./path/to/your/database.db.db", "--mcp"]

Alternatively, you can add it to your Cursor configuration file directly.

Direct JSON-RPC Usage

The MCP server runs as a single process that handles multiple JSON-RPC requests over stdin/stdout. Here's how to interact with it directly:

Example with In-Memory Database

cat << 'EOF' | tursodb --mcp
{"jsonrpc": "2.0", "id": 1, "method": "initialize", "params": {"protocolVersion": "2024-11-05", "capabilities": {}, "clientInfo": {"name": "client", "version": "1.0"}}}
{"jsonrpc": "2.0", "id": 2, "method": "tools/call", "params": {"name": "schema_change", "arguments": {"query": "CREATE TABLE users (id INTEGER, name TEXT, email TEXT)"}}}
{"jsonrpc": "2.0", "id": 3, "method": "tools/call", "params": {"name": "list_tables", "arguments": {}}}
{"jsonrpc": "2.0", "id": 4, "method": "tools/call", "params": {"name": "insert_data", "arguments": {"query": "INSERT INTO users VALUES (1, 'Alice', 'alice@example.com')"}}}
{"jsonrpc": "2.0", "id": 5, "method": "tools/call", "params": {"name": "execute_query", "arguments": {"query": "SELECT * FROM users"}}}
EOF

Example with Existing Database

# Working with an existing database file
cat << 'EOF' | tursodb mydb.db --mcp
{"jsonrpc": "2.0", "id": 1, "method": "initialize", "params": {"protocolVersion": "2024-11-05", "capabilities": {}, "clientInfo": {"name": "client", "version": "1.0"}}}
{"jsonrpc": "2.0", "id": 2, "method": "tools/call", "params": {"name": "list_tables", "arguments": {}}}
EOF

Contributing

We'd love to have you contribute to Turso Database! Please check out the contribution guide to get started.

Found a data corruption bug? Get up to $1,000.00

SQLite is loved because it is the most reliable database in the world. The next evolution of SQLite has to match or surpass this level of reliability. Turso is built with Deterministic Simulation Testing from the ground up, and is also tested by Antithesis.

Even during Alpha, if you find a bug that leads to a data corruption and demonstrate how our simulator failed to catch it, you can get up to $1,000.00. As the project matures we will increase the size of the prize, and the scope of the bugs.

More details here.

You can see an example of an awarded case on #2049.

Turso core staff are not eligible.

FAQ

Is Turso Database ready for production use?

Turso Database is currently under heavy development and is not ready for production use.

How is Turso Database different from Turso's libSQL?

Turso Database is a project to build the next evolution of SQLite in Rust, with a strong open contribution focus and features like native async support, vector search, and more. The libSQL project is also an attempt to evolve SQLite in a similar direction, but through a fork rather than a rewrite.

Rewriting SQLite in Rust started as an unassuming experiment, and due to its incredible success, replaces libSQL as our intended direction. At this point, libSQL is production ready, Turso Database is not - although it is evolving rapidly. More details here.

Publications

  • Pekka Enberg, Sasu Tarkoma, Jon Crowcroft Ashwin Rao (2024). Serverless Runtime / Database Co-Design With Asynchronous I/O. In EdgeSys 24. [PDF]
  • Pekka Enberg, Sasu Tarkoma, and Ashwin Rao (2023). Towards Database and Serverless Runtime Co-Design. In CoNEXT-SW 23. [PDF] [Slides]

License

This project is licensed under the MIT license.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Turso Database by you, shall be licensed as MIT, without any additional terms or conditions.

Partners

Thanks to all the partners of Turso!

Contributors

Thanks to all the contributors to Turso Database!

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