要使用Apollo-Server将订阅功能连接到Postgres数据库，需要遵循以下步骤：

1. 首先，确保已安装必要的依赖项。在终端中运行以下命令：

npm install apollo-server apollo-server-express graphql pg

2. 创建一个GraphQL模式文件（例如schema.js），定义你的GraphQL类型和订阅操作。以下是一个简单的示例：

const { gql } = require('apollo-server');

const typeDefs = gql`
  type Post {
    id: ID!
    title: String!
    content: String!
  }

  type Query {
    posts: [Post]
  }

  type Mutation {
    createPost(title: String!, content: String!): Post
  }

  type Subscription {
    postAdded: Post
  }
`;

module.exports = typeDefs;

3. 创建一个Apollo-Server实例，并将其连接到Postgres数据库。在你的入口文件（例如index.js）中添加以下代码：

const { ApolloServer, PubSub } = require('apollo-server');
const { Pool } = require('pg');
const typeDefs = require('./schema');

const pubsub = new PubSub();

// 创建Postgres数据库连接池
const pool = new Pool({
  user: 'your_username',
  host: 'your_host',
  database: 'your_database',
  password: 'your_password',
  port: 5432,
});

// 从数据库获取帖子
const getPosts = async () => {
  const client = await pool.connect();
  const result = await client.query('SELECT * FROM posts');
  client.release();
  return result.rows;
};

// 将帖子插入到数据库
const createPost = async (title, content) => {
  const client = await pool.connect();
  const result = await client.query(
    'INSERT INTO posts (title, content) VALUES ($1, $2) RETURNING *',
    [title, content]
  );
  client.release();
  return result.rows[0];
};

const resolvers = {
  Query: {
    posts: () => getPosts(),
  },
  Mutation: {
    createPost: (_, { title, content }) => createPost(title, content),
  },
  Subscription: {
    postAdded: {
      subscribe: () => pubsub.asyncIterator(['POST_ADDED']),
    },
  },
};

const server = new ApolloServer({ typeDefs, resolvers });

server.listen().then(({ url }) => {
  console.log(`Server running at ${url}`);
});

4. 在resolver中，使用PubSub来发布新的帖子。在createPost函数中添加以下代码：

const createPost = async (title, content) => {
  const client = await pool.connect();
  const result = await client.query(
    'INSERT INTO posts (title, content) VALUES ($1, $2) RETURNING *',
    [title, content]
  );
  const post = result.rows[0];
  // 发布新的帖子
  pubsub.publish('POST_ADDED', { postAdded: post });
  client.release();
  return post;
};

现在，你可以使用Apollo-Server来订阅Postgres数据库中的数据了。例如，在前端应用中使用subscriptions-transport-ws库来订阅postAdded操作。

希望这可以帮助到你！