mysql怎么提高查询速度慢

-- 不推荐
SELECT * FROM users WHERE age > 25;

-- 推荐
SELECT id, name, email FROM users WHERE age > 25;

CREATE INDEX idx_age ON users(age);

CREATE TABLE users (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    email VARCHAR(100)
);

CREATE TABLE orders (
    id INT PRIMARY KEY,
    user_id INT,
    amount DECIMAL(10, 2),
    FOREIGN KEY (user_id) REFERENCES users(id)
);

import redis
import pymysql

# 连接 Redis
redis_client = redis.StrictRedis(host='localhost', port=6379, db=0)

# 连接 MySQL
mysql_conn = pymysql.connect(host='localhost', user='user', password='password', db='mydb')
mysql_cursor = mysql_conn.cursor()

def get_user_by_id(user_id):
    # 尝试从 Redis 缓存中获取数据
    cached_user = redis_client.get(f'user:{user_id}')
    if cached_user:
        return cached_user

    # 如果缓存中没有数据，从 MySQL 中获取
    mysql_cursor.execute("SELECT * FROM users WHERE id = %s", (user_id,))
    user = mysql_cursor.fetchone()

    # 将数据存入 Redis 缓存
    redis_client.set(f'user:{user_id}', user)

    return user