一张表有年龄，身高两个字段，如何用SQL取每个年龄段身高最高的那一条数据

如果你想从一张表中获取每个年龄段（比如按每5岁划分）的最高身高数据，可以使用SQL的`ROW_NUMBER()`或者分组查询结合`LIMIT`来实现。这里假设表名为`users`，字段分别为`age`和`height`，且没有年龄相同的身高更高的记录。以下是两种常见的方式：

**方法一：MySQL（不支持窗口函数）**

SELECT *
FROM (
  SELECT age, height,
         @row_num := IF(@prev_age = age, @row_num + 1, 1) AS row_num,
         @prev_age := age
  FROM users, (SELECT @row_num := 0, @prev_age := NULL) t
  ORDER BY age, height DESC
) ranked_users
WHERE row_num = 1;

**方法二：PostgreSQL、SQL Server 或者支持窗口函数的数据库**

WITH ranked_users AS (
  SELECT age, height,
         ROW_NUMBER() OVER (PARTITION BY FLOOR(age / 5) ORDER BY height DESC) as row_num
  FROM users
)
SELECT * FROM ranked_users WHERE row_num = 1;