I have a table that has the following schema:

```
ID | FirstName | Surname | TransmissionID | CaptureDateTime
1  | Billy     | Goat    | ABCDEF         | 2018-09-20 13:45:01.098
2  | Jonny     | Cash    | ABCDEF         | 2018-09-20 13:45.01.108
3  | Sally     | Sue     | ABCDEF         | 2018-09-20 13:45:01.298
4  | Jermaine  | Cole    | PQRSTU         | 2018-09-20 13:45:01.398
5  | Mike      | Smith   | PQRSTU         | 2018-09-20 13:45:01.498

```

There are well over 70,000 records and they store logs of transmissions to a web-service. What I'd like to know is how would I go about writing a script that would select the distinct `TransmissionID` values and also show the timespan between the earliest `CaptureDateTime` record and the latest record? Essentially I'd like to see what the rate of records the web-service is reading & writing.

Is it even possible to do so in a single `SELECT` statement or should I just create a stored procedure or report in code? I don't know where to start aside from `SELECT DISTINCT TransmissionID` for this sort of query. 

Here's what I have so far (I'm stuck on the time calculation)

```
SELECT DISTINCT [TransmissionID],
        COUNT(*) as 'Number of records'
  FROM [log_table]
  GROUP BY [TransmissionID]
  HAVING COUNT(*) > 1

```

Not sure how to get the difference between the first and last record with the same `TransmissionID` I would like to get a result set like:

```
TransmissionID | TimeToCompletion | Number of records |
ABCDEF         |            2.001 |             5000  |

```