MySQL 中 ROW_NUMBER() 函数最佳实践

ROW_NUMBER() OVER (
    [PARTITION BY 分组字段]
    ORDER BY 排序字段 [ASC|DESC]
)

-- 查询第3页数据（每页10条）
WITH paged_data AS (
    SELECT 
        id, name, 
        ROW_NUMBER() OVER (ORDER BY id) AS row_num
    FROM users
)
SELECT * 
FROM paged_data 
WHERE row_num BETWEEN 21 AND 30;

-- 保留最新记录（假设 create_time 为时间戳）
DELETE FROM orders
WHERE (id, product_id) IN (
    SELECT id, product_id FROM (
        SELECT 
            id, product_id,
            ROW_NUMBER() OVER (
                PARTITION BY product_id 
                ORDER BY create_time DESC
            ) AS rn
        FROM orders
    ) t 
    WHERE rn > 1  -- 删除重复项，保留最新一条
);

-- 获取每个部门薪资前3名
SELECT *
FROM (
    SELECT 
        name, department, salary,
        ROW_NUMBER() OVER (
            PARTITION BY department 
            ORDER BY salary DESC
        ) AS dept_rank
    FROM employees
) ranked
WHERE dept_rank <= 3;

-- 按日期生成订单流水号（格式：YYYYMMDD-0001）
SELECT 
    order_id,
    CONCAT(
        DATE_FORMAT(create_time, '%Y%m%d'), 
        '-', 
        LPAD(ROW_NUMBER() OVER (
            PARTITION BY DATE(create_time) 
            ORDER BY create_time
        ), 4, '0')
    ) AS serial_num
FROM orders;

-- 对比三种函数
SELECT 
    score,
    ROW_NUMBER() OVER (ORDER BY score DESC) AS row_num,
    RANK() OVER (ORDER BY score DESC) AS rank,
    DENSE_RANK() OVER (ORDER BY score DESC) AS dense_rank
FROM exam_scores;

CREATE INDEX idx_dept_salary ON employees(department, salary DESC);

-- 仅处理2023年数据
SELECT *
FROM (
    SELECT 
        order_id, amount,
        ROW_NUMBER() OVER (ORDER BY amount DESC) AS rn
    FROM orders
    WHERE YEAR(order_date) = 2023  -- 先过滤再排序
) t
WHERE rn <= 100;

-- 优化前（性能差）
SELECT * FROM (
    SELECT *, ROW_NUMBER() OVER (...) AS rn
    FROM large_table
) t WHERE rn <= 100;
-- 优化后（直接使用LIMIT，若逻辑允许）
SELECT *, ROW_NUMBER() OVER (...) AS rn
FROM large_table
ORDER BY ...
LIMIT 100;

-- 按部门分组排序
SELECT 
    department, name, salary,
    @row_num := IF(
        @current_dept = department, 
        @row_num + 1, 
        1
    ) AS row_num,
    @current_dept := department AS dummy
FROM employees
ORDER BY department, salary DESC;

WITH ranked_products AS (
    SELECT 
        product_id,
        ROW_NUMBER() OVER (PARTITION BY category ORDER BY sales DESC) AS rn
    FROM products
)
SELECT * FROM ranked_products WHERE rn = 1;