LC 5852016年的投资Investments in 2016　中等

Insurance 表记录保单的 tiv_2015、tiv_2016 与经纬度；对 tiv_2015 与其他保单相同、且位置坐标唯一的保单，求 tiv_2016 总和，保留 2 位小数。

思路 两个子查询：GROUP BY + HAVING 计数筛选，(lat,lon) 行元组 IN。

SELECT ROUND(SUM(tiv_2016), 2) AS tiv_2016
FROM Insurance
WHERE tiv_2015 IN (
  SELECT tiv_2015 FROM Insurance
  GROUP BY tiv_2015 HAVING COUNT(*) > 1
) AND (lat, lon) IN (
  SELECT lat, lon FROM Insurance
  GROUP BY lat, lon HAVING COUNT(*) = 1
);

数据表：Insurance　·　关键字：对 tiv_2015 与其他保单相同、且位置坐标唯一的保单，求 tiv_2016 总和，保留 2 位小数