如何将多个查询结果与列名一起显示？

Question

我有四个查询，数据取自同一张表。

select sum(unit_sold) as total_unit_sold 
from tewt 
where order_priority = 'HH'

union all

select avg(unit_sold) as average_unit_sold 
from tewt 
where order_priority = 'H'

union all

select max(unit_sold) as maximum_unit_sold 
from tewt 
where order_priority = 'M'

union all

select min(unit_sold) as minimum_unit_sold 
from tewt 
where order_priority = 'L';

我使用“Union All”来描述所有没有行名和列名的结果。

结果：

total_unit_sold (numeric)
1. 2401
2. 5362.00
3. 7699
4. 6184

但我不知道如何将它们与每个结果的列/行名称一起显示。

任何帮助将不胜感激。

谢谢

Answer 1

将每个选择作为列表达式，而不是UNION ALL将它们放在一起；这允许您为每个子选择分配一个列名。

SELECT
    (select sum(unit_sold) from tewt where order_priority='HH') as total_unit_sold,
    (select avg(unit_sold) from tewt where order_priority='H') as average_unit_sold,
    (select max(unit_sold) from tewt where order_priority='M') as maximum_unit_sold,
    (select min(unit_sold) from tewt where order_priority='L') as minimum_unit_sold;

不清楚您所说的“行名”是什么意思 - 您有 4 个值，因此它或者是 4 行 x 1 列，就像您已经拥有的一样，或者是 1 行 x 4 列，如上所示。如果您想要的是 4x4，行标记为“HH”、“H”、“M”、“L”，列标记为现有查询中的列，新单元格为 NULLS，这也是可能的，但涉及更多&我如果是这样的话，我会让你澄清一下。

Answer 2

如果您对 4 种情况使用 CASE 表达式，则可以在 1 个查询中完成：

SELECT order_priority, 
       CASE order_priority
         WHEN 'HH' THEN 'total_unit_sold' 
         WHEN 'H' THEN 'average_unit_sold'
         WHEN 'M' THEN 'maximum_unit_sold'
         WHEN 'L' THEN 'minimum_unit_sold'
       END description, 
       CASE order_priority
         WHEN 'HH' THEN SUM(unit_sold) 
         WHEN 'H' THEN AVG(unit_sold) 
         WHEN 'M' THEN MAX(unit_sold) 
         WHEN 'L' THEN MIN(unit_sold) 
       END amount
FROM tewt 
WHERE order_priority IN ('HH', 'H', 'M', 'L')
GROUP BY order_priority 

如果您希望将所有值作为 1 行中的 4 列，您可以使用条件聚合来实现：

SELECT SUM(CASE WHEN order_priority = 'HH' THEN unit_sold END) total_unit_sold,
       AVG(CASE WHEN order_priority = 'H' THEN unit_sold END) average_unit_sold,
       MAX(CASE WHEN order_priority = 'M' THEN unit_sold END) maximum_unit_sold,
       MIN(CASE WHEN order_priority = 'L' THEN unit_sold END) minimum_unit_sold       
FROM tewt 
WHERE order_priority IN ('HH', 'H', 'M', 'L');

或者：

SELECT SUM(unit_sold) FILTER (WHERE order_priority = 'HH') total_unit_sold,
       AVG(unit_sold) FILTER (WHERE order_priority = 'H') average_unit_sold,
       MAX(unit_sold) FILTER (WHERE order_priority = 'M') maximum_unit_sold,
       MIN(unit_sold) FILTER (WHERE order_priority = 'L') minimum_unit_sold       
FROM tewt 
WHERE order_priority IN ('HH', 'H', 'M', 'L');

如果'HH'、'H'、'M' 和'L' 是order_priority 的唯一可能值，则可以删除WHERE 子句。

Answer 3

在 Postgres 中，您将使用条件聚合，它使用 filter 子句：

select sum(unit_sold) filter (where order_priority = 'HH') as hh_total_unit_sold,
       sum(unit_sold) filter (where order_priority = 'H') as h_total_unit_sold,
       sum(unit_sold) filter (where order_priority = 'M') as m_total_unit_sold,
       sum(unit_sold) filter (where order_priority = 'L') as l_total_unit_sold       
from tewt ;