Sql

Question

我正在尝试编写 sql，它会给我出现在类别 'blue' 和 'red' 中但不在任何其他类别中的独特设备的数量。

下面是我的简单示例。这个问题的答案是 3 台设备（设备 1、2、5）。

如果有人能给我提示，我将不胜感激。谢谢你。

 device | category 
--------+----------
      1 | blue
      2 | red
      3 | black
      4 | yellow
      4 | blue
      5 | red
      5 | blue

Answer 1

一种方法是将您的 table 加入到识别匹配设备的聚合查询中。

WITH cte AS (
    SELECT Device
    FROM yourTable
    GROUP BY Device
    HAVING SUM(CASE WHEN category NOT IN ('blue', 'red') THEN 1 ELSE 0 END) = 0
)

SELECT t1.Device, t1.Category
FROM yourTable t1
INNER JOIN cte t2
    ON t1.Device = t2.Device;

我们也可以用SUM作为解析函数：

SELECT Device, category
FROM
(
    SELECT Device, category,
        SUM(CASE WHEN category NOT IN ('blue', 'red') THEN 1 ELSE 0 END) OVER
            (PARTITION BY Device) color_sum
    FROM yourTable
) t
WHERE color_sum = 0;

Demo

Answer 2

使用bool_and():

with my_table(device, category) as (
values 
    (1, 'blue'),
    (2, 'red'),
    (3, 'black'),
    (4, 'yellow'),
    (4, 'blue'),
    (5, 'red'),
    (5, 'blue')
)

select device, bool_and(category in ('red', 'blue'))
from my_table
group by device
order by device;

 device | bool_and 
--------+----------
      1 | t
      2 | t
      3 | f
      4 | f
      5 | t
(5 rows)

您的查询可能如下所示：

select device
from my_table
group by device
having bool_and(category in ('red', 'blue'))
order by device;

Answer 3

select distinct device from Test
where category in ('blue','red')
except
select distinct device from Test
where category in (select distinct category from test
                     where category not in ('blue','red'))

或者如果您需要计数：

select count(*)
from
(select distinct device from Test
where category in ('blue','red')
except
select distinct device from Test
where category in (select distinct category from test
                     where category not in ('blue','red'))) a

Sql - 过滤特定类别

Sql - Filtering on certain category

postgresql

where-clause

Demo