Text-to-SQL

In this tutorial, we’ll see how to implement an agent that leverages SQL using smolagents.

Let’s start with the golden question: why not keep it simple and use a standard text-to-SQL pipeline?

A standard text-to-sql pipeline is brittle, since the generated SQL query can be incorrect. Even worse, the query could be incorrect, but not raise an error, instead giving some incorrect/useless outputs without raising an alarm.

👉 Instead, an agent system is able to critically inspect outputs and decide if the query needs to be changed or not, thus giving it a huge performance boost.

Let’s build this agent! 💪

First, we setup the SQL environment:

from sqlalchemy import (
    create_engine,
    MetaData,
    Table,
    Column,
    String,
    Integer,
    Float,
    insert,
    inspect,
    text,
)

engine = create_engine("sqlite:///:memory:")
metadata_obj = MetaData()

# create city SQL table
table_name = "receipts"
receipts = Table(
    table_name,
    metadata_obj,
    Column("receipt_id", Integer, primary_key=True),
    Column("customer_name", String(16), primary_key=True),
    Column("price", Float),
    Column("tip", Float),
)
metadata_obj.create_all(engine)

rows = [
    {"receipt_id": 1, "customer_name": "Alan Payne", "price": 12.06, "tip": 1.20},
    {"receipt_id": 2, "customer_name": "Alex Mason", "price": 23.86, "tip": 0.24},
    {"receipt_id": 3, "customer_name": "Woodrow Wilson", "price": 53.43, "tip": 5.43},
    {"receipt_id": 4, "customer_name": "Margaret James", "price": 21.11, "tip": 1.00},
]
for row in rows:
    stmt = insert(receipts).values(**row)
    with engine.begin() as connection:
        cursor = connection.execute(stmt)

Build our agent

Now let’s make our SQL table retrievable by a tool.

The tool’s description attribute will be embedded in the LLM’s prompt by the agent system: it gives the LLM information about how to use the tool. This is where we want to describe the SQL table.

inspector = inspect(engine)
columns_info = [(col["name"], col["type"]) for col in inspector.get_columns("receipts")]

table_description = "Columns:\n" + "\n".join([f"  - {name}: {col_type}" for name, col_type in columns_info])
print(table_description)

Columns:
  - receipt_id: INTEGER
  - customer_name: VARCHAR(16)
  - price: FLOAT
  - tip: FLOAT

Now let’s build our tool. It needs the following: (read the tool doc for more detail)

A docstring with an Args: part listing arguments.
Type hints on both inputs and output.

from smolagents import tool

@tool
def sql_engine(query: str) -> str:
    """
    Allows you to perform SQL queries on the table. Returns a string representation of the result.
    The table is named 'receipts'. Its description is as follows:
        Columns:
        - receipt_id: INTEGER
        - customer_name: VARCHAR(16)
        - price: FLOAT
        - tip: FLOAT

    Args:
        query: The query to perform. This should be correct SQL.
    """
    output = ""
    with engine.connect() as con:
        rows = con.execute(text(query))
        for row in rows:
            output += "\n" + str(row)
    return output

Now let us create an agent that leverages this tool.

We use the CodeAgent, which is transformers.agents’ main agent class: an agent that writes actions in code and can iterate on previous output according to the ReAct framework.

The model is the LLM that powers the agent system. HfApiModel allows you to call LLMs using HF’s Inference API, either via Serverless or Dedicated endpoint, but you could also use any proprietary API.

from smolagents import CodeAgent, HfApiModel

agent = CodeAgent(
    tools=[sql_engine],
    model=HfApiModel("meta-llama/Meta-Llama-3.1-8B-Instruct"),
)
agent.run("Can you give me the name of the client who got the most expensive receipt?")

Level 2: Table joins

Now let’s make it more challenging! We want our agent to handle joins across multiple tables.

So let’s make a second table recording the names of waiters for each receipt_id!

table_name = "waiters"
receipts = Table(
    table_name,
    metadata_obj,
    Column("receipt_id", Integer, primary_key=True),
    Column("waiter_name", String(16), primary_key=True),
)
metadata_obj.create_all(engine)

rows = [
    {"receipt_id": 1, "waiter_name": "Corey Johnson"},
    {"receipt_id": 2, "waiter_name": "Michael Watts"},
    {"receipt_id": 3, "waiter_name": "Michael Watts"},
    {"receipt_id": 4, "waiter_name": "Margaret James"},
]
for row in rows:
    stmt = insert(receipts).values(**row)
    with engine.begin() as connection:
        cursor = connection.execute(stmt)

Since we changed the table, we update the SQLExecutorTool with this table’s description to let the LLM properly leverage information from this table.

updated_description = """Allows you to perform SQL queries on the table. Beware that this tool's output is a string representation of the execution output.
It can use the following tables:"""

inspector = inspect(engine)
for table in ["receipts", "waiters"]:
    columns_info = [(col["name"], col["type"]) for col in inspector.get_columns(table)]

    table_description = f"Table '{table}':\n"

    table_description += "Columns:\n" + "\n".join([f"  - {name}: {col_type}" for name, col_type in columns_info])
    updated_description += "\n\n" + table_description

print(updated_description)

Since this request is a bit harder than the previous one, we’ll switch the LLM engine to use the more powerful Qwen/Qwen2.5-Coder-32B-Instruct!

sql_engine.description = updated_description

agent = CodeAgent(
    tools=[sql_engine],
    model=HfApiModel("Qwen/Qwen2.5-Coder-32B-Instruct"),
)

agent.run("Which waiter got more total money from tips?")

It directly works! The setup was surprisingly simple, wasn’t it?

This example is done! We’ve touched upon these concepts:

Building new tools.
Updating a tool’s description.
Switching to a stronger LLM helps agent reasoning.

✅ Now you can go build this text-to-SQL system you’ve always dreamt of! ✨

< > Update on GitHub