如何查询vertica中聚合的百分比

Question

Table 产品

productId type
1          A
2          A
3          A
4          B
5          B
6          C

我想要的：

type     perc
A         0.5
B         0.33
C         0.17

我们可以这样写一个简单的查询：

Select type, cnt/(select count(*) from product) AS perc
FROM (
select type, count(*) as cnt
from product
group by type
 ) nested

但是vertica不支持不相关的subselect

需要别人的帮助！

Answer 1

Vertica 支持相关和非相关子查询，即使您可能对连接谓词有限制。

因此，您上面的查询有效。而且 - 你猜怎么着 - 即使你使用缩进，它也会继续工作：

SQL> SELECT
         type
       , cnt/( select count (*) FROM product ) AS perc
     FROM
         ( SELECT type, count (*) as cnt
           FROM product
           GROUP BY type
         ) nested ;
 type |         perc         
------+----------------------
 C    | 0.166666666666666667
 A    | 0.500000000000000000
 B    | 0.333333333333333333
(3 rows)

当然你可以用不同的方式重写它。例如：

SQL> SELECT
        a.type
      , a.cnt/b.tot as perc
    FROM
      ( SELECT type , count (*) as cnt
        FROM product
        GROUP BY type ) a
    CROSS JOIN
      ( SELECT count (*) AS tot
        FROM product ) b
    ORDER BY 1
    ;
 type |         perc         
------+----------------------
 A    | 0.500000000000000000
 B    | 0.333333333333333333
 C    | 0.166666666666666667
(3 rows)

Answer 2

你也可以使用解析函数，在这个应用程序中它很乱，但工作：

WITH product AS (
          select 1 as productId, 'A' as type
union all select 2, 'A'
union all select 3, 'A'
union all select 4, 'B'
union all select 5, 'B'
union all select 6, 'C'
)

SELECT distinct /* distinct because analytic functions don't reduce row count like aggregate functions */
  type, count(*) over (partition by type) / count(*) over ()
FROM product;

 type |         perc         
------+----------------------
 A    | 0.500000000000000000
 B    | 0.333333333333333333
 C    | 0.166666666666666667

count(*) over (partition by type) 统计每种类型；

count(*) over () 计算所有内容，所以得到总计数

如何查询vertica中聚合的百分比

how to query the percentage of aggregate in vertica

sql

database

vertica