I have the following query: 

```
SELECT 
   c.callID,
   c.time,
   c.duration,
   (case_statement) AS inquiry_type
FROM calls AS c

```

My question is on regard to build the case\_statement. There is another table `call_hco` that associates `calls` and `hco` together. 

I need the `case_statement` to be if `callID` has `hco = 61` on `call_hco` table then `inquiry_type` will be "Service". If `callID` has `hco = 52` or `hco = 54` or `hco = 56` then `inquiry_type` will be "Sales", otherwise `inquiry_type` will be "NULL". 

It is worth mentioning that if you query on `call_hco` for a specific `callID` it can return one or more rows since the same `callID` could be associated with more than one `hco`.

Query results should look something like:

```
callID    time    duration(seconds)    inquiry_type
12        15:35         55                 Service
15        10:56         135                Sales
16        18:36         45                 NULL
18        13:00         234                Sales

```

Any help is really appreciated.