Cannot step through asynchronous iterator manually

[Michael Torrie]

On 01/30/2016 01:22 AM, Frank Millman wrote:
> There are times when I want to execute a SELECT statement, and test for 
> three possibilities -
>     - if no rows are returned, the object does not exist
>     - if one row is returned, the object does exist
>     - if more that one row is returned, raise an exception

Is there a reason you cannot get SQL to answer this question for you?
Something like:

SELECT count(some_field) WHERE condition

That will always return one row, with one field that will either be 0,
1, or more than 1.