I have table (called `STAT`) for tracking work order status change, like this:

```
| WORKNUM    | STATUS    | CHANGE_DATE             |
+------------+-----------+-------------------------+
| WO-1057004 | APPROVED  | 2018-05-25 05:53:34.157 |
| WO-1057004 | COMPLETED | 2018-06-13 06:45:4O.244 |
| WO-1057004 | REVIEWED  | 2018-07-05 03:53:35.231 |

```

I need to find time in days it took from 'COMPLETED' status to 'REVIEWED' status, for the same work order - i.e. the difference in `CHANGE_DATE` between these two statuses in days.

I'm using SQL Server 2016.

I don’t know where to begin, but I am looking for something like this:

```
| WORKNUM    | STATUS    | CHANGE_DATE             | TIME_TAKEN |
+------------+-----------+-------------------------+------------+
| WO-1057004 | APPROVED  | 2018-05-25 05:53:34.157 |     0      |
| WO-1057004 | COMPLETED | 2018-06-13 06:45:4O.244 |    19      |
| WO-1057004 | REVIEWED  | 2018-07-05 03:53:35.231 |    22      |

```

Your help is much appreciated.

Thanks.