Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:

Convert text to sql: What are the different names of all reviewers whose ratings do not have a date field? | movie : mid , title , year , director | reviewer : rid , name | rating : rid , mid , stars , ratingdate | rating.rid = reviewer.rid | rating.mid = movie.mid | 

### Response:

select distinct _ from _ where _ | select distinct name from reviewer join rating on reviewer.rid = rating.rid where ratingdate = 'null'