带大小写的 SQL 计数

Question

我正在尝试做这样的事情。

signal_status    signal_count
---------------|---------------
Average        |    10   
Good           |    11  
Very Poor      |     4  
Poor           |     5  
Below Average  |     8  
Excellent      |    13

设备总数为 51，其计数应采用上面在 signal_count 中定义的方式。

我得到的是 signal_status （只有第一列）。现在我也想要计数，但无法根据设备获得计数。这是我试图获取第一列的查询。

select signal_status from (select case 
when signal_info <= 31 and signal_info > 24 then 'Excellent' 
when signal_info <= 24 and signal_info > 19 then 'Good' 
when signal_info <= 19 and signal_info > 14 then 'Average' 
when signal_info <= 14 and signal_info > 9 then 'Below Average' 
when signal_info <= 9 and signal_info > 5 then 'Poor' 
when signal_info <= 5 and signal_info > 0 then 'Very Poor' end 
AS signal_status from data_channel) AS WTH group by signal_status;

我尝试了所有可能的方法，但无法获取所需的结果。 data_channel 表包含以下列： sno (PK), device_id, signal_info, datetime 我希望它与 table_1 加入以加入 device_id。 table_1 包含以下列： device_id (PK), device_name

基本上我想要做的是我希望所有设备的信号强度为平均好或差的设备的计数，但我得到的是表中的总记录，而不是基于最近的设备 signal_info。 如果不清楚，请原谅。

注意：使用 SQL Server 而不是 MySQL

Answer 1

试试这个：

SELECT signal_status, COUNT(DISTINCT device_id) signal_count FROM (
    SELECT 
        CASE 
            WHEN signal_info <= 31 and signal_info > 24 THEN 'Excellent' 
            WHEN signal_info <= 24 and signal_info > 19 THEN 'Good' 
            WHEN signal_info <= 19 and signal_info > 14 THEN 'Average' 
            WHEN signal_info <= 14 and signal_info > 9 THEN 'Below Average' 
            WHEN signal_info <= 9 and signal_info > 5 THEN 'Poor' 
            WHEN signal_info <= 5 and signal_info > 0 THEN 'Very Poor' 
        END signal_status, device_id 
    FROM data_channel
) AS WTH 
GROUP BY signal_status

Answer 2

您就快到了 - 您只是在选择列表中错过了对 count 的呼叫：

SELECT   signal_status, 
         COUNT(*) -- Here!
FROM     (SELECT CASE WHEN signal_info <= 31 AND signal_info > 24 THEN 'Excellent' 
                      WHEN signal_info <= 24 AND signal_info > 19 THEN 'Good' 
                      WHEN signal_info <= 19 AND signal_info > 14 THEN 'Average' 
                      WHEN signal_info <= 14 AND signal_info > 9  THEN 'Below Average' 
                      WHEN signal_info <= 9  AND signal_info > 5  THEN 'Poor' 
                      WHEN signal_info <= 5  AND signal_info > 0  THEN 'Very Poor'
                 END  AS signal_status 
          FROM data_channel) AS wth
GROUP BY signal_status;

Answer 3

以上答案都是正确的，看看样本数据和输出。如果您有不同的要求，请提供示例数据。

--drop table #data_channel

create table #data_channel
(
sno int identity primary key,
device_id varchar(100), 
signal_info int
)

insert into #data_channel values
('A',24),
('B',14),
('C',24),
('D',31),
('E',1),
('F',13),
('G',20),
('H',12)--,('A',24),('A',24),('A',24),('A',24),('A',24),('A',24),

查询

select signal_status,Count(*) as signalcount
 from (select case 
when signal_info <= 31 and signal_info > 24 then 'Excellent' 
when signal_info <= 24 and signal_info > 19 then 'Good' 
when signal_info <= 19 and signal_info > 14 then 'Average' 
when signal_info <= 14 and signal_info > 9 then 'Below Average' 
when signal_info <= 9 and signal_info > 5 then 'Poor' 
when signal_info <= 5 and signal_info > 0 then 'Very Poor' end 
AS signal_status from #data_channel) AS WTH group by signal_status;

输出

signal_status   signalcount
Below Average   3
Excellent   1
Good    3
Very Poor   1

Answer 4

试试这个：

SELECT signal_status, COUNT(device_id) signal_count 
FROM 
(
    SELECT CASE 
                WHEN signal_info <= 31 and signal_info > 24 THEN 'Excellent' 
                WHEN signal_info <= 24 and signal_info > 19 THEN 'Good' 
                WHEN signal_info <= 19 and signal_info > 14 THEN 'Average' 
                WHEN signal_info <= 14 and signal_info > 9 THEN 'Below Average' 
                WHEN signal_info <= 9 and signal_info > 5 THEN 'Poor' 
                WHEN signal_info <= 5 and signal_info > 0 THEN 'Very Poor' 
            END signal_status
           ,device_id
           ,ROW_NUMBER() OVER (PARTITION BY device_id ORDER BY [datetime] DESC) AS [RowID]
    FROM data_channel
) AS WTH
WHERE [RowID] = 1
GROUP BY signal_status