SQL - 无论记录如何，如何选择最后 5 个值

Question

我需要粉碎记录，所以我有每个字段的最新 5 个值，不包括空值和空白。预期的结果将产生一个这样的表格：

1. HT |重量 |体重指数 |英国石油公司人力资源 | RR

2. 72 | 148 | 20.07 | 120/70 | 68 | 16

3. 72 | 152 | 20.61 | 120/80 | 68 | 16

4. 72 | 154 | 20.88 | 120/68 | 70 | 16

5. ...

   这里是已经按日期排序的示例数据集。

Answer 1

SQL 表代表无序 集合。没有最后五行之类的东西，除非一列提供了该信息。假设您有这样的专栏。

这是你想要的吗？

select t.*
from t
where ht is not null and wt is not null and bmi is not null
order by ? desc
limit 5;

这是你想要的吗？

编辑：

我想我误解了这个问题。您似乎希望每列独立。为此，我认为union all 和group by 可能比较合适：

select max(ht) as ht,
       max(wt) as wt,
       max(bmi) as bmi,
       . . .
from ((select (@rnh := @rnh + 1) as rn, ht, null as wt, null as bmi, . . .
       from t cross join (select @rnh := 0) params
       where ht is not null
       order by ? desc
       limit 5
      ) union all
      (select (@rnw := @rnw + 1) as rn, null, wt, null as bmi, . . .
       from t cross join (select @rnw := 0) params
       where wt is not null
       order by ? desc
       limit 5
      ) union all
      (select (@rnb := @rnb + 1) as rn, null as ht, null as wt, bmi, . . .
       from t cross join (select @rnb := 0) params
       where ht is not null
       order by ? desc
       limit 5
      ) union all
      . . .
     ) x
group by rn;

? 用于指定排序的列。