sql - SQL：在选择中选择作为子查询

Question

我有以下声明：

select 
    product_name as ShortestLength = (select top 1 product_name, len(fact_name) Value_Length 
                                      from table 
                                      order by Value_Length, fact_name ASC)

返回此输出：

shortestlength
PS

我想将此结果添加到另一个选择语句中：

select
    'Product' as Column_Name,
    avg(case when product is null then 1.000 else 0 end) * 100 as PctMissing,
    count(product) as TotalCount,
    count(distinct product) as UniqueCount
from 
    table

所以结果将是：

列名	失踪	总数	唯一计数	最短长度
产品	5.100	181186	15	附言

我应该在我的初始选择语句中添加什么？

Answer 1

您可以使用条件聚合：

select 'Product' as Column_Name,
        avg(case when t.product is null then 1.000 else 0 end)*100 as PctMissing,
        count(t.product) as TotalCount,
        count(distinct t.product) as UniqueCount,
        max(case when seqnum = 1 then product_name end) as shortest_length
from (select t.*,
             row_number() over (order by len(fact_name), fact_name) as seqnum
      from table t 
     ) t

这假设这两个table引用实际上是同一个表。

Answer 2

您可以将第一个查询用作子查询来代替 select 语句中的列：

select
    'Product' as Column_Name,
    avg(case when product is null then 1.000 else 0 end)*100 as PctMissing,
    count(product) as TotalCount,
    count(distinct product) as UniqueCount,
(select top 1 product_name from table order by Value_Length, fact_name ASC) as ShortestLength 
from table