GROUP BY无法处理时间戳数据-Oracle SQL

Question

I have some data regarding some of our work orders. The data looks like this:

| OrderNumber | StepNumber |  StepStart  |  StepFinish |
|:-----------:|:----------:|:-----------:|:-----------:|
|     100     |      1     |  9:00:00 AM | 12:00:00 PM |
|     100     |      2     | 12:00:00 PM |  1:00:00 PM |
|     100     |      3     |  1:30:00 PM |  1:35:00 PM |
|     100     |      4     |  1:50:00 PM |  5:00:00 PM |
|     100     |      5     |  8:45:00 PM | 11:55:00 PM |
|     200     |      1     |  5:00:00 AM |  5:30:00 AM |
|     200     |      2     |  6:00:00 AM |  6:30:00 AM |
|     200     |      3     |  7:00:00 AM |  7:30:00 AM |
|     200     |      4     |  8:00:00 AM |  8:30:00 AM |
|     200     |      5     |  9:00:00 AM |  9:30:00 AM |
|     200     |      6     | 10:00:00 AM | 10:30:00 AM |
|     200     |      7     | 11:00:00 AM | 11:30:00 AM |
|     200     |      8     | 12:00:00 PM | 12:30:00 PM |

I am trying to GROUP BY the OrderNumber to create the "total time" it took to finish by subtracting the finish time of it's LAST step and the start time of its FIRST step.

My end result would look like this:

| OrderNumber | TimetoFinish |
|:-----------:|:------------:|
|     100     |     0.62     |
|     200     |    0.3125    |

(Yes, I know those decimals are not time. That is the total "days" it took to finish as sometimes the orders can take multiple days. The real data is a date and timestamp, this is spoofed data. Same rules apply)

I have tried the following:

SELECT
  OrderNumber,
  MEDIAN(ABS(MIN(StepStart - StepFinish))) AS TimetoFinish

FROM
  orders

GROUP BY
  OrderNumber

But get an:

ORA-00937: not a single-group group function

Which I don't understand, because I am only selecting one non-aggregate column (the OrderNumber ).

I have an SQL Fiddle here. Why is the GROUP BY not working?

Answer 1

Where is the median() coming from? Just use:

SELECT OrderNumber,
       (MAX(StepFinish) - MIN(StepStart)) AS TimetoFinish
FROM orders o
GROUP BY OrderNumber;

This assumes that StepFinish and StepStart are stored in some reasonable format. The above should work on date and timestamp for instance.