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// 優(yōu)化前：一次三表關(guān)聯(lián)查詢String sql = "SELECT o.order_id, c.customer_name, p.product_name " +             "FROM orders o " +             "JOIN customers c ON o.customer_id = c.customer_id " +             "JOIN products p ON o.product_id = p.product_id";
// 優(yōu)化后：分步查詢// 1. 查詢訂單基本信息String orderSql = "SELECT order_id, customer_id, product_id FROM orders";// 2. 根據(jù)customer_id查詢客戶信息String customerSql = "SELECT customer_id, customer_name FROM customers WHERE customer_id IN (?)";// 3. 根據(jù)product_id查詢商品信息String productSql = "SELECT product_id, product_name FROM products WHERE product_id IN (?)";

@Servicepublic class OrderService {    @Autowired    private RedisTemplate redisTemplate;     public OrderDTO getOrderDetail(Long orderId) {        // 1. 先從緩存獲取        String cacheKey = "order:" + orderId;        OrderDTO orderDTO = redisTemplate.opsForValue().get(cacheKey);         if (orderDTO != null) {            return orderDTO;        }         // 2. 緩存未命中，查詢數(shù)據(jù)庫        OrderDTO result = queryFromDatabase(orderId);         // 3. 寫入緩存        redisTemplate.opsForValue().set(cacheKey, result, 1, TimeUnit.HOURS);         return result;    }}

-- 優(yōu)化前的訂單表結(jié)構(gòu)CREATE TABLE orders (    order_id BIGINT PRIMARY KEY,    customer_id BIGINT,    product_id BIGINT,    -- 其他字段);
-- 優(yōu)化后的訂單表結(jié)構(gòu)（增加冗余字段）CREATE TABLE orders (    order_id BIGINT PRIMARY KEY,    customer_id BIGINT,    customer_name VARCHAR(100),  -- 冗余客戶名稱    product_id BIGINT,    product_name VARCHAR(100),   -- 冗余商品名稱    -- 其他字段);

-- 為關(guān)聯(lián)字段創(chuàng)建索引CREATE INDEX idx_customer_id ON orders(customer_id);CREATE INDEX idx_product_id ON orders(product_id);
-- 考慮創(chuàng)建復(fù)合索引CREATE INDEX idx_customer_product ON orders(customer_id, product_id);