适用场景

窗口函数适用场景: 对分组统计结果中的每一条记录进行计算的场景下, 使用窗口函数更好, 注意, 是每一条；因为MySQL的普通聚合函数的结果(如 group by)是每一组只有一条记录。

准备数据

创建表

create table app_product
(
    id            bigint auto_increment comment '主键'
        primary key,
    product_name     varchar(100)  null comment '产品名称',
    product_type    varchar(100)  null comment '产品类型',
    price          int  null comment '价格'
)
    comment '产品表';

准备数据：

INSERT INTO app_product (id, product_name, product_type, price) VALUES (1, 'A1', 'A', 20);
INSERT INTO app_product (id, product_name, product_type, price) VALUES (2, 'A2', 'A', 40);
INSERT INTO app_product (id, product_name, product_type, price) VALUES (3, 'A3', 'A', 60);
INSERT INTO app_product (id, product_name, product_type, price) VALUES (4, 'B1', 'B', 10);
INSERT INTO app_product (id, product_name, product_type, price) VALUES (5, 'B2', 'B', 30);
INSERT INTO app_product (id, product_name, product_type, price) VALUES (6, 'B3', 'B', 50);
INSERT INTO app_product (id, product_name, product_type, price) VALUES (7, 'C1', 'C', 23);
INSERT INTO app_product (id, product_name, product_type, price) VALUES (8, 'C4', 'C', 57);

使用示例

使用别名

SELECT *,row_number() OVER w AS priceRank
FROM app_product
 WINDOW w AS (PARTITION BY product_type ORDER BY price DESC);

序号函数

按照产品分类，按照价格排序。

row_number()顺序展示编号

SELECT
	*,
	row_number() OVER (PARTITION BY product_type ORDER BY price DESC) AS priceRank
FROM
	app_product;

获取每个分类的前3个价格高的产品

select * from (SELECT
	*,
	row_number() OVER (PARTITION BY product_type ORDER BY price DESC) AS priceRank
FROM
	app_product) t where priceRank <=3;

rank()，同等级同序号，序号不连续。

SELECT
	*,
	RANK() OVER (PARTITION BY product_type ORDER BY price DESC) AS priceRank
FROM
	app_product;

dense_rank()，同等级同序号，序号连续。

SELECT
	*,
	dense_rank() OVER (PARTITION BY product_type ORDER BY price DESC) AS priceRank
FROM
	app_product;

分布函数

percent_rank()，等级值百分比。（rank-1)/(rows-1)

SELECT *,
       percent_rank() OVER (PARTITION BY product_type ORDER BY price DESC) AS priceRank
FROM app_product;

cume_dist()，累积分布值。小于等于rank值的行数/总行数

SELECT *,
       cume_dist() OVER (PARTITION BY product_type ORDER BY price DESC) AS priceRank
FROM app_product;

前后函数

LAG(expr, n) - 返回当前行的前n行(本组内)的expr值

SELECT *,
       lag(price,1) OVER (PARTITION BY product_type ORDER BY price DESC) AS pre_price
FROM app_product;

LEAD(expr, n)返回当前行的后n行(本组)的expr值

SELECT *,
       lead(price,1) OVER (PARTITION BY product_type ORDER BY price DESC) AS post_price
FROM app_product;

首位行数

first_value(expr)获取分组内第一行数据 , last_value(expr)获取分组内最后一行数据，nth_value(price,2)获取分组内第n行的数据。

SELECT *,
       first_value(price) OVER w first_price,last_value(price) OVER w last_price,nth_value(price,2) over w nTh_price
FROM app_product WINDOW w AS (PARTITION BY product_type ORDER BY price DESC);