计算SQL查询中前缀的匹配数

Question

I have a table in an SQL server that looks like the one below and I want to count the number of unique occurrences where specific prefixes are used in the data column, like "21:00:00".

Dataset:

+-------------------------+
|          data           |
+-------------------------+
| 21:00:00:24:ff:5e:3a:bd |
| 50:01:43:80:18:6b:2a:4c |
| 21:00:00:1b:32:0f:a7:54 |
| 10:00:00:90:fa:a8:da:2a |
+-------------------------+

Desired query output:

+----------+----------+----------+
| 21:00:00 | 50:01:43 | 10:00:00 |
+----------+----------+----------+
|        2 |        1 |        1 |
+----------+----------+----------+

I have been able to get the query to count a single prefix at a time by using this:

SELECT COUNT(DISTINCT wwpn) AS "21:00:00" FROM table WHERE wwpn LIKE '21:00:00%'

However, I want to count multiple prefixes as shown in the desired query output.

Answer 1

I've been waiting for someone to do a dynamic pivot (like Matt said in the comments) but no one has done it yet : (...I tried it myself and this is what I managed...

Query :

DECLARE @cols AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX)

select @cols = STUFF((SELECT distinct ',' + LEFT(QUOTENAME(data), 9) + ']' 
        FROM DataTable
        FOR XML PATH(''), TYPE
        ).value('.', 'NVARCHAR(MAX)') 
    ,1,1,'')

set @query = N'SELECT ' + @cols + N' from 
         (
            select LEFT(data, 8) as data, COUNT(*) as count
            from DataTable
            GROUP BY LEFT(data, 8)
        ) x
        pivot 
        (
            max(count)
            for data in (' + @cols + N')
        ) p '

exec sp_executesql @query;

Results:

10:00:00 | 21:00:00 | 50:01:43
---------|----------|---------
    1    |    2     |    1
---------|----------|---------

Answer 2

If you know the prefixes in advance then you can do something simple like this;

Create test data;

CREATE TABLE #TestData (FieldName nvarchar(50))
INSERT INTO #TestData
VALUES
 ('21:00:00:24:ff:5e:3a:bd')
,('50:01:43:80:18:6b:2a:4c')
,('21:00:00:1b:32:0f:a7:54')
,('10:00:00:90:fa:a8:da:2a')

Query

SELECT
SUM(CASE WHEN FieldName LIKE '21:00:00%' THEN 1 ELSE 0 END) [21:00:00]
,SUM(CASE WHEN FieldName LIKE '50:01:43%' THEN 1 ELSE 0 END) [50:01:43]
,SUM(CASE WHEN FieldName LIKE '10:00:00%' THEN 1 ELSE 0 END) [10:00:00]
FROM #TestData

Result

21:00:00    50:01:43    10:00:00
2           1           1

Answer 3

Use this query:

SELECT LEFT([Data], 8) as prefix, count(*) as cnt
    FROM tableName
    GROUP BY LEFT([Data], 8);