Still playing around with tables and queries but need some help with a SQL Server query.

I have a table that looks like this.

```
VMName   | DiskType   | Status      | Result
---------+------------+-------------+---------
TestVM1  |  OS        | Completed   | 
TestVM1  |  Data      | Completed   | 
TestVM2  |  OS        | Failed      | 
TestVM2  |  Data      | Completed   | 
TestVM2  |  Data      | Completed   | 

```

In the results column, I'd like to have it say "Completed" **if** both the OS and data disks have a status of completed.

If however, the OS disk shows failed, then the results column should show failed for all the disks of that VM.

Like this.

```
VMName   | DiskType   | Status      | Result
---------+------------+-------------+---------
TestVM1  |  OS        | Completed   | Completed
TestVM1  |  Data      | Completed   | Completed
TestVM2  |  OS        | Failed      | Failed
TestVM2  |  Data      | Completed   | Failed
TestVM2  |  Data      | Completed   | Failed

```

I tried cobbling together a query, but not sure what I'm doing wrong as it doesn't do anything.

```
UPDATE working_table t1
SET Result = 'Failed'
WHERE disktype = 'OS' AND 
      status = 'Failed' AND
      NOT EXISTS (SELECT 1 FROM working_table t2 WHERE t1.VMname = t2.VMname);

```