PostgreSQL RANK() 窗口函数实例详解

RANK() OVER (ORDER BY column [ASC|DESC] [NULLS {FIRST|LAST}])

张三: 100分 → 第 1 名
李四: 100分 → 第 1 名  ← 并列
王五: 95分  → 第 3 名  ← 跳过第 2 名！
赵六: 90分  → 第 4 名

SELECT 
    name,
    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 students;
-- 结果:
-- name  | score | row_num | rank | dense_rank
-- ------+-------+---------+------+------------
-- 张三  | 100   | 1       | 1    | 1
-- 李四  | 100   | 2       | 1    | 1      ← 并列第一
-- 王五  | 95    | 3       | 3    | 2      ← RANK 跳过 2
-- 赵六  | 90    | 4       | 4    | 3

SELECT 
    emp_name,
    sales_amount,
    RANK() OVER (ORDER BY sales_amount DESC) AS rank
FROM sales_performance
WHERE rank <= 10;  -- 前 10 名（可能超过 10 人，因为有并列）

SELECT * FROM (
    SELECT 
        student_id,
        name,
        score,
        RANK() OVER (ORDER BY score DESC) AS rank
    FROM exam_scores
) t
WHERE rank = 1;  -- 所有并列第一的学生

SELECT 
    emp_name,
    sales_amount,
    RANK() OVER (ORDER BY sales_amount DESC) AS rank,
    CASE 
        WHEN RANK() OVER (ORDER BY sales_amount DESC) <= 3 THEN '🥇 金牌'
        WHEN RANK() OVER (ORDER BY sales_amount DESC) <= 10 THEN '🥈 银牌'
        WHEN RANK() OVER (ORDER BY sales_amount DESC) <= 50 THEN ' 铜牌'
        ELSE '参与奖'
    END AS award
FROM sales_performance;

SELECT 
    order_no,
    created_at,
    RANK() OVER (ORDER BY order_no) AS expected_no,
    order_no - RANK() OVER (ORDER BY order_no) AS gap
FROM orders
WHERE order_no - RANK() OVER (ORDER BY order_no) > 0;  -- 有缺口的地方

SELECT * FROM (
    SELECT 
        dept_name,
        emp_name,
        sales_amount,
        RANK() OVER (PARTITION BY dept_name ORDER BY sales_amount DESC) AS rank
    FROM employees
) t
WHERE rank <= 3;  -- 每个部门前 3 名（含并列）

SELECT 
    emp_name,
    sales_amount,
    SUM(sales_amount) OVER (ORDER BY sales_amount DESC) AS running_total,
    SUM(sales_amount) OVER () AS grand_total,
    ROUND(
        SUM(sales_amount) OVER (ORDER BY sales_amount DESC)::DECIMAL / 
        SUM(sales_amount) OVER () * 100, 
        2
    ) AS cumulative_percent
FROM sales_performance;

-- 查看前 20% 的销售人员贡献了多少业绩
SELECT * FROM (
    SELECT 
        emp_name,
        sales_amount,
        RANK() OVER (ORDER BY sales_amount DESC) AS rank,
        COUNT(*) OVER () AS total_count
    FROM sales_performance
) t
WHERE rank::DECIMAL / total_count <= 0.2;  -- 前 20%

-- ❌ ROW_NUMBER 会只保留一条
DELETE FROM orders
WHERE id IN (
    SELECT id FROM (
        SELECT 
            id,
            order_no,
            ROW_NUMBER() OVER (PARTITION BY order_no ORDER BY id) AS rn
        FROM orders
    ) t
    WHERE rn > 1
);
-- ✅ RANK 会保留所有并列的
DELETE FROM orders
WHERE id IN (
    SELECT id FROM (
        SELECT 
            id,
            order_no,
            RANK() OVER (PARTITION BY order_no, amount, created_at ORDER BY id) AS rn
        FROM orders
    ) t
    WHERE rn > 1
);

SELECT 
    student_id,
    name,
    status,
    CASE 
        WHEN status = '请假' THEN NULL
        ELSE RANK() OVER (
            PARTITION BY CASE WHEN status != '请假' THEN 1 ELSE 0 END 
            ORDER BY student_id
        )
    END AS seat_number
FROM students
ORDER BY student_id;

RANK() OVER (
    PARTITION BY column1, column2  -- 可选：分组依据
    ORDER BY column3 DESC          -- 必填：排序规则
)

-- ❌ 慢：多次调用 RANK()
SELECT 
    emp_name,
    RANK() OVER (ORDER BY sales DESC) AS rank,
    CASE 
        WHEN RANK() OVER (ORDER BY sales DESC) <= 10 THEN '优秀'
        ELSE '普通'
    END AS level
FROM employees;
-- ✅ 快：用子查询或 CTE
WITH ranked AS (
    SELECT 
        emp_name,
        sales,
        RANK() OVER (ORDER BY sales DESC) AS rank
    FROM employees
)
SELECT 
    emp_name,
    rank,
    CASE WHEN rank <= 10 THEN '优秀' ELSE '普通' END AS level
FROM ranked;

-- 为 ORDER BY 字段创建索引
CREATE INDEX idx_sales_perf_sales ON sales_performance (sales_amount DESC);
-- 这样 RANK() 计算会更快
SELECT 
    emp_name,
    sales_amount,
    RANK() OVER (ORDER BY sales_amount DESC) AS rank
FROM sales_performance;

-- ❌ 错误
SELECT * FROM employees
WHERE RANK() OVER (ORDER BY salary DESC) <= 10;
-- ✅ 正确：用子查询
SELECT * FROM (
    SELECT *, RANK() OVER (ORDER BY salary DESC) AS rank
    FROM employees
) t
WHERE rank <= 10;

-- ❌ 错误：RANK 必须有排序规则
RANK() OVER (PARTITION BY dept_id)
-- ✅ 正确
RANK() OVER (PARTITION BY dept_id ORDER BY salary DESC)

-- 假设有 3 个人并列第 1
SELECT 
    name,
    score,
    RANK() OVER (ORDER BY score DESC) AS rank
FROM students;
-- 结果:
-- name  | score | rank
-- ------+-------+------
-- 张三  | 100   | 1
-- 李四  | 100   | 1
-- 王五  | 100   | 1
-- 赵六  | 95    | 4    ← 不是 2！跳过了 2 和 3

RANK 排名会跳号，并列之后空位跑
奥运奖牌最典型，金银铜牌不颠倒
若要排名更紧凑，DENSE_RANK 来效劳
分页去重用 ROW，场景不同选对宝

-- 基本模板
SELECT * FROM (
    SELECT 
        字段列表,
        RANK() OVER (
            PARTITION BY 分组字段     -- 可选
            ORDER BY 排序字段 DESC    -- 必填
        ) AS rank
    FROM 表名
) t
WHERE rank <= N;  -- 前 N 名（含并列）