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在本教程中，我们将使用 LangGraph 构建一个能够回答 SQL 数据库相关问题的自定义智能体。 LangChain 提供了内置的智能体实现，基于 LangGraph 原语实现。如果需要更深度的自定义，可以直接在 LangGraph 中实现智能体。本指南演示了一个 SQL 智能体的示例实现。如需实用入门指南，请参阅使用高级 LangChain 抽象构建 SQL 智能体。
构建 SQL 数据库的问答系统需要执行模型生成的 SQL 查询。这样做存在固有风险。请确保你的数据库连接权限始终尽可能地限制在智能体所需的最小范围内。这将减轻（但不能消除）构建模型驱动系统的风险。
预构建智能体让我们可以快速上手，但我们依赖系统提示来约束其行为——例如，我们指示智能体始终从”列出表”工具开始，并始终在执行查询前运行查询检查工具。 在 LangGraph 中，我们可以通过自定义智能体来实施更高程度的控制。在这里，我们实现了一个简单的 ReAct 智能体设置，为特定的工具调用配置了专用节点。我们将使用与预构建智能体相同的[状态]。

​
概念

我们将涵盖以下概念：
  • 用于从 SQL 数据库读取数据的工具
  • LangGraph 图 API，包括状态、节点、边和条件边。
  • 人机协作流程

​
设置

​
安装

pip install langchain  langgraph  langchain-community

​
LangSmith

设置 LangSmith 来检查链或智能体的内部运行情况。然后设置以下环境变量： 
export LANGSMITH_TRACING="true"
export LANGSMITH_API_KEY="..."

​
1. 选择 LLM

选择一个支持工具调用的模型：
👉 Read the OpenAI chat model integration docs
pip install -U "langchain[openai]"

import os
from langchain.chat_models import init_chat_model

os.environ["OPENAI_API_KEY"] = "sk-..."

model = init_chat_model("gpt-5.4")
示例中显示的输出使用了 OpenAI。

​
2. 配置数据库

你将为本教程创建一个 SQLite 数据库。SQLite 是一个轻量级数据库，易于设置和使用。我们将加载 chinook 数据库，这是一个代表数字媒体商店的示例数据库。 为方便起见，我们已将数据库（Chinook.db）托管在公共 GCS 存储桶中。 
import requests, pathlib

url = "https://storage.googleapis.com/benchmarks-artifacts/chinook/Chinook.db"
local_path = pathlib.Path("Chinook.db")

if local_path.exists():
    print(f"{local_path} already exists, skipping download.")
else:
    response = requests.get(url)
    if response.status_code == 200:
        local_path.write_bytes(response.content)
        print(f"File downloaded and saved as {local_path}")
    else:
        print(f"Failed to download the file. Status code: {response.status_code}")
我们将使用 langchain_community 包中提供的便捷 SQL 数据库包装器与数据库交互。该包装器提供了一个简单的接口来执行 SQL 查询并获取结果： 
from langchain_community.utilities import SQLDatabase

db = SQLDatabase.from_uri("sqlite:///Chinook.db")

print(f"Dialect: {db.dialect}")
print(f"Available tables: {db.get_usable_table_names()}")
print(f'Sample output: {db.run("SELECT * FROM Artist LIMIT 5;")}')

Dialect: sqlite
Available tables: ['Album', 'Artist', 'Customer', 'Employee', 'Genre', 'Invoice', 'InvoiceLine', 'MediaType', 'Playlist', 'PlaylistTrack', 'Track']
Sample output: [(1, 'AC/DC'), (2, 'Accept'), (3, 'Aerosmith'), (4, 'Alanis Morissette'), (5, 'Alice In Chains')]

​
3. 添加数据库交互工具

使用 langchain_community 包中的 SQLDatabase 包装器与数据库交互。该包装器提供了一个简单的接口来执行 SQL 查询并获取结果： 
from langchain_community.agent_toolkits import SQLDatabaseToolkit

toolkit = SQLDatabaseToolkit(db=db, llm=model)

tools = toolkit.get_tools()

for tool in tools:
    print(f"{tool.name}: {tool.description}\n")

sql_db_query: 此工具的输入是详细且正确的 SQL 查询，输出是数据库的结果。如果查询不正确，将返回错误消息。如果返回了错误，请重写查询、检查查询并重试。如果遇到 'field list' 中的 Unknown column 'xxxx' 问题，请使用 sql_db_schema 查询正确的表字段。

sql_db_schema: 此工具的输入是逗号分隔的表名列表，输出是这些表的模式和示例行。请确保先调用 sql_db_list_tables 确认表确实存在！示例输入：table1, table2, table3

sql_db_list_tables: 输入为空字符串，输出是数据库中以逗号分隔的表列表。

sql_db_query_checker: 使用此工具在执行查询前仔细检查查询是否正确。始终在使用 sql_db_query 执行查询前使用此工具！

​
4. 定义应用步骤

我们为以下步骤构建专用节点：
  • 列出数据库表
  • 调用”获取模式”工具
  • 生成查询
  • 检查查询
将这些步骤放在专用节点中让我们可以 (1) 在需要时强制工具调用，以及 (2) 自定义与每个步骤关联的提示。 
from typing import Literal

from langchain.messages import AIMessage
from langchain_core.runnables import RunnableConfig
from langgraph.graph import END, START, MessagesState, StateGraph
from langgraph.prebuilt import ToolNode


get_schema_tool = next(tool for tool in tools if tool.name == "sql_db_schema")
get_schema_node = ToolNode([get_schema_tool], name="get_schema")

run_query_tool = next(tool for tool in tools if tool.name == "sql_db_query")
run_query_node = ToolNode([run_query_tool], name="run_query")


# 示例：创建预定义的工具调用
def list_tables(state: MessagesState):
    tool_call = {
        "name": "sql_db_list_tables",
        "args": {},
        "id": "abc123",
        "type": "tool_call",
    }
    tool_call_message = AIMessage(content="", tool_calls=[tool_call])

    list_tables_tool = next(tool for tool in tools if tool.name == "sql_db_list_tables")
    tool_message = list_tables_tool.invoke(tool_call)
    response = AIMessage(f"Available tables: {tool_message.content}")

    return {"messages": [tool_call_message, tool_message, response]}


# 示例：强制模型创建工具调用
def call_get_schema(state: MessagesState):
    # 注意 LangChain 强制所有模型接受 `tool_choice="any"`
    # 以及 `tool_choice=<工具名称字符串>`。
    llm_with_tools = model.bind_tools([get_schema_tool], tool_choice="any")
    response = llm_with_tools.invoke(state["messages"])

    return {"messages": [response]}


generate_query_system_prompt = """
You are an agent designed to interact with a SQL database.
Given an input question, create a syntactically correct {dialect} query to run,
then look at the results of the query and return the answer. Unless the user
specifies a specific number of examples they wish to obtain, always limit your
query to at most {top_k} results.

You can order the results by a relevant column to return the most interesting
examples in the database. Never query for all the columns from a specific table,
only ask for the relevant columns given the question.

DO NOT make any DML statements (INSERT, UPDATE, DELETE, DROP etc.) to the database.
""".format(
    dialect=db.dialect,
    top_k=5,
)


def generate_query(state: MessagesState):
    system_message = {
        "role": "system",
        "content": generate_query_system_prompt,
    }
    # 这里不强制工具调用，允许模型在获得解答时自然响应。
    llm_with_tools = model.bind_tools([run_query_tool])
    response = llm_with_tools.invoke([system_message] + state["messages"])

    return {"messages": [response]}


check_query_system_prompt = """
You are a SQL expert with a strong attention to detail.
Double check the {dialect} query for common mistakes, including:
- Using NOT IN with NULL values
- Using UNION when UNION ALL should have been used
- Using BETWEEN for exclusive ranges
- Data type mismatch in predicates
- Properly quoting identifiers
- Using the correct number of arguments for functions
- Casting to the correct data type
- Using the proper columns for joins

If there are any of the above mistakes, rewrite the query. If there are no mistakes,
just reproduce the original query.

You will call the appropriate tool to execute the query after running this check.
""".format(dialect=db.dialect)


def check_query(state: MessagesState):
    system_message = {
        "role": "system",
        "content": check_query_system_prompt,
    }

    # 生成一个人工用户消息来检查
    tool_call = state["messages"][-1].tool_calls[0]
    user_message = {"role": "user", "content": tool_call["args"]["query"]}
    llm_with_tools = model.bind_tools([run_query_tool], tool_choice="any")
    response = llm_with_tools.invoke([system_message, user_message])
    response.id = state["messages"][-1].id

    return {"messages": [response]}

​
5. 实现智能体

现在我们可以使用图 API将这些步骤组装成工作流。我们在查询生成步骤定义了一个条件边，如果生成了查询则路由到查询检查器，如果没有工具调用则结束（即 LLM 已对查询作出响应）。 
def should_continue(state: MessagesState) -> Literal[END, "check_query"]:
    messages = state["messages"]
    last_message = messages[-1]
    if not last_message.tool_calls:
        return END
    else:
        return "check_query"


builder = StateGraph(MessagesState)
builder.add_node(list_tables)
builder.add_node(call_get_schema)
builder.add_node(get_schema_node, "get_schema")
builder.add_node(generate_query)
builder.add_node(check_query)
builder.add_node(run_query_node, "run_query")

builder.add_edge(START, "list_tables")
builder.add_edge("list_tables", "call_get_schema")
builder.add_edge("call_get_schema", "get_schema")
builder.add_edge("get_schema", "generate_query")
builder.add_conditional_edges(
    "generate_query",
    should_continue,
)
builder.add_edge("check_query", "run_query")
builder.add_edge("run_query", "generate_query")

agent = builder.compile()
下面我们可视化应用： 
from IPython.display import Image, display
from langchain_core.runnables.graph import CurveStyle, MermaidDrawMethod, NodeStyles

display(Image(agent.get_graph().draw_mermaid_png()))
SQL 智能体图 现在我们可以调用图： 
question = "Which genre on average has the longest tracks?"

for step in agent.stream(
    {"messages": [{"role": "user", "content": question}]},
    stream_mode="values",
):
    step["messages"][-1].pretty_print()

================================ Human Message =================================

Which genre on average has the longest tracks?
================================== Ai Message ==================================

Available tables: Album, Artist, Customer, Employee, Genre, Invoice, InvoiceLine, MediaType, Playlist, PlaylistTrack, Track
================================== Ai Message ==================================
Tool Calls:
  sql_db_schema (call_yzje0tj7JK3TEzDx4QnRR3lL)
 Call ID: call_yzje0tj7JK3TEzDx4QnRR3lL
  Args:
    table_names: Genre, Track
================================= Tool Message =================================
Name: sql_db_schema


CREATE TABLE "Genre" (
	"GenreId" INTEGER NOT NULL,
	"Name" NVARCHAR(120),
	PRIMARY KEY ("GenreId")
)

/*
3 rows from Genre table:
GenreId	Name
1	Rock
2	Jazz
3	Metal
*/


CREATE TABLE "Track" (
	"TrackId" INTEGER NOT NULL,
	"Name" NVARCHAR(200) NOT NULL,
	"AlbumId" INTEGER,
	"MediaTypeId" INTEGER NOT NULL,
	"GenreId" INTEGER,
	"Composer" NVARCHAR(220),
	"Milliseconds" INTEGER NOT NULL,
	"Bytes" INTEGER,
	"UnitPrice" NUMERIC(10, 2) NOT NULL,
	PRIMARY KEY ("TrackId"),
	FOREIGN KEY("MediaTypeId") REFERENCES "MediaType" ("MediaTypeId"),
	FOREIGN KEY("GenreId") REFERENCES "Genre" ("GenreId"),
	FOREIGN KEY("AlbumId") REFERENCES "Album" ("AlbumId")
)

/*
3 rows from Track table:
TrackId	Name	AlbumId	MediaTypeId	GenreId	Composer	Milliseconds	Bytes	UnitPrice
1	For Those About To Rock (We Salute You)	1	1	1	Angus Young, Malcolm Young, Brian Johnson	343719	11170334	0.99
2	Balls to the Wall	2	2	1	U. Dirkschneider, W. Hoffmann, H. Frank, P. Baltes, S. Kaufmann, G. Hoffmann	342562	5510424	0.99
3	Fast As a Shark	3	2	1	F. Baltes, S. Kaufman, U. Dirkscneider & W. Hoffman	230619	3990994	0.99
*/
================================== Ai Message ==================================
Tool Calls:
  sql_db_query (call_cb9ApLfZLSq7CWg6jd0im90b)
 Call ID: call_cb9ApLfZLSq7CWg6jd0im90b
  Args:
    query: SELECT Genre.Name, AVG(Track.Milliseconds) AS AvgMilliseconds FROM Track JOIN Genre ON Track.GenreId = Genre.GenreId GROUP BY Genre.GenreId ORDER BY AvgMilliseconds DESC LIMIT 5;
================================== Ai Message ==================================
Tool Calls:
  sql_db_query (call_DMVALfnQ4kJsuF3Yl6jxbeAU)
 Call ID: call_DMVALfnQ4kJsuF3Yl6jxbeAU
  Args:
    query: SELECT Genre.Name, AVG(Track.Milliseconds) AS AvgMilliseconds FROM Track JOIN Genre ON Track.GenreId = Genre.GenreId GROUP BY Genre.GenreId ORDER BY AvgMilliseconds DESC LIMIT 5;
================================= Tool Message =================================
Name: sql_db_query

[('Sci Fi & Fantasy', 2911783.0384615385), ('Science Fiction', 2625549.076923077), ('Drama', 2575283.78125), ('TV Shows', 2145041.0215053763), ('Comedy', 1585263.705882353)]
================================== Ai Message ==================================

The genre with the longest tracks on average is "Sci Fi & Fantasy," with an average track length of approximately 2,911,783 milliseconds. Other genres with relatively long tracks include "Science Fiction," "Drama," "TV Shows," and "Comedy."
查看上述运行的 LangSmith 追踪。

​
6. 实现人机协作审核

在执行智能体的 SQL 查询之前检查它们以避免任何意外操作或低效率是明智的做法。 这里我们利用 LangGraph 的人机协作功能在执行 SQL 查询之前暂停运行并等待人工审核。使用 LangGraph 的持久化层，我们可以无限期地暂停运行（或者至少在持久化层存活期间）。 让我们用一个接收人工输入的节点来包装 sql_db_query 工具。我们可以使用 interrupt 函数来实现。下面，我们允许输入来批准工具调用、编辑其参数或提供用户反馈。 
from langchain_core.runnables import RunnableConfig
from langchain.tools import tool
from langgraph.types import interrupt

@tool(
    run_query_tool.name,
    description=run_query_tool.description,
    args_schema=run_query_tool.args_schema
)
def run_query_tool_with_interrupt(config: RunnableConfig, **tool_input):
    request = {
        "action": run_query_tool.name,
        "args": tool_input,
        "description": "Please review the tool call"
    }
    response = interrupt([request])
    # 批准工具调用
    if response["type"] == "accept":
        tool_response = run_query_tool.invoke(tool_input, config)
    # 更新工具调用参数
    elif response["type"] == "edit":
        tool_input = response["args"]["args"]
        tool_response = run_query_tool.invoke(tool_input, config)
    # 用用户反馈回复 LLM
    elif response["type"] == "response":
        user_feedback = response["args"]
        tool_response = user_feedback
    else:
        raise ValueError(f"Unsupported interrupt response type: {response['type']}")

    return tool_response

# 重新定义工具节点以使用中断版本
run_query_node = ToolNode([run_query_tool_with_interrupt], name="run_query")
上述实现遵循了更广泛的人机协作指南中的工具中断示例。有关详细信息和替代方案，请参阅该指南。
现在让我们重新组装图。我们将用人工审核替代程序化检查。注意我们现在包含了一个检查点器；这是暂停和恢复运行所必需的。 
from langgraph.checkpoint.memory import InMemorySaver

def should_continue(state: MessagesState) -> Literal[END, "run_query"]:
    messages = state["messages"]
    last_message = messages[-1]
    if not last_message.tool_calls:
        return END
    else:
        return "run_query"

builder = StateGraph(MessagesState)
builder.add_node(list_tables)
builder.add_node(call_get_schema)
builder.add_node(get_schema_node, "get_schema")
builder.add_node(generate_query)
builder.add_node(run_query_node, "run_query")

builder.add_edge(START, "list_tables")
builder.add_edge("list_tables", "call_get_schema")
builder.add_edge("call_get_schema", "get_schema")
builder.add_edge("get_schema", "generate_query")
builder.add_conditional_edges(
    "generate_query",
    should_continue,
)
builder.add_edge("run_query", "generate_query")

checkpointer = InMemorySaver()
agent = builder.compile(checkpointer=checkpointer)
我们可以像之前一样调用图。这次，执行会被中断： 
import json

config = {"configurable": {"thread_id": "1"}}

question = "Which genre on average has the longest tracks?"

for step in agent.stream(
    {"messages": [{"role": "user", "content": question}]},
    config,
    stream_mode="values",
):
    if "messages" in step:
        step["messages"][-1].pretty_print()
    elif "__interrupt__" in step:
        action = step["__interrupt__"][0]
        print("已中断：")
        for request in action.value:
            print(json.dumps(request, indent=2))
    else:
        pass

...

已中断：
{
  "action": "sql_db_query",
  "args": {
    "query": "SELECT Genre.Name, AVG(Track.Milliseconds) AS AvgLength FROM Track JOIN Genre ON Track.GenreId = Genre.GenreId GROUP BY Genre.Name ORDER BY AvgLength DESC LIMIT 5;"
  },
  "description": "Please review the tool call"
}
我们可以使用 Command 来接受或编辑工具调用： 
from langgraph.types import Command


for step in agent.stream(
    Command(resume={"type": "accept"}),
    # Command(resume={"type": "edit", "args": {"query": "..."}}),
    config,
    stream_mode="values",
):
    if "messages" in step:
        step["messages"][-1].pretty_print()
    elif "__interrupt__" in step:
        action = step["__interrupt__"][0]
        print("已中断：")
        for request in action.value:
            print(json.dumps(request, indent=2))
    else:
        pass

================================== Ai Message ==================================
Tool Calls:
  sql_db_query (call_t4yXkD6shwdTPuelXEmY3sAY)
 Call ID: call_t4yXkD6shwdTPuelXEmY3sAY
  Args:
    query: SELECT Genre.Name, AVG(Track.Milliseconds) AS AvgLength FROM Track JOIN Genre ON Track.GenreId = Genre.GenreId GROUP BY Genre.Name ORDER BY AvgLength DESC LIMIT 5;
================================= Tool Message =================================
Name: sql_db_query

[('Sci Fi & Fantasy', 2911783.0384615385), ('Science Fiction', 2625549.076923077), ('Drama', 2575283.78125), ('TV Shows', 2145041.0215053763), ('Comedy', 1585263.705882353)]
================================== Ai Message ==================================

The genre with the longest average track length is "Sci Fi & Fantasy" with an average length of about 2,911,783 milliseconds. Other genres with long average track lengths include "Science Fiction," "Drama," "TV Shows," and "Comedy."
有关详细信息，请参阅人机协作指南。

​
后续步骤

查看评估图指南，了解如何使用 LangSmith 评估 LangGraph 应用，包括像这样的 SQL 智能体。
将这些文档连接到 Claude、VSCode 等，通过 MCP 获取实时答案。
在 GitHub 上编辑此页面或提交 issue。