refactor(ch5): align filenames and update corresponding README sections

m05_langchain_advanced/s03_sql_agent.py

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+from config import OPENAI_API_KEY
+import sqlite3
+from langchain_openai import ChatOpenAI
+from langchain_community.agent_toolkits import create_sql_agent
+from langchain_community.utilities import SQLDatabase  # 导入 SQLDatabase
+import os
+
+# 配置llm
+llm = ChatOpenAI(
+    model="deepseek-chat",
+    api_key=OPENAI_API_KEY,
+    base_url="https://api.deepseek.com"
+)
+
+# 创建一个临时的数据库--用于演示
+db_file = "test_sql.db"
+if os.path.exists(db_file):
+    os.remove(db_file)
+conn = sqlite3.connect(db_file)
+cursor = conn.cursor()
+cursor.execute("CREATE TABLE users (id INT,name TEXT,age INT);")
+cursor.execute("INSERT INTO users (id,name,age) VALUES (1,'Alice',30);")
+cursor.execute("INSERT INTO users (id,name,age) VALUES (2,'Bob',25);")
+conn.commit()
+conn.close()
+
+# 连接数据库 -- LangChain 使用 SQLAlchemy URI (连接方式)
+db_uri = f'sqlite:///{db_file}'
+db = SQLDatabase.from_uri(db_uri)
+
+# 创建sqlAgent -- 一键完成，无需定义tools，仅告诉它使用openai-tools,即Tool Calling(工具调用)模式
+agent_executor = create_sql_agent(
+    llm=llm,
+    db=db,
+    agent_type="openai-tools",
+    verbose=True
+)
+
+# 运行
+response = agent_executor.invoke({"input":"告诉我Alice多大了？"})
+print(response['output'])
+
+# 清理
+db._engine.dispose() # 关闭连接池，避免文件被占用
+if os.path.exists(db_file):
+    os.remove(db_file)