sql - Returning highest DATETIME from row with particular column data -

i trying select highest datetime specific request code:

this query i'm using:

select submittime    [qtraxadmin].[qt_request]   submittime in (select max(submittime)                          [qtraxadmin].[qt_request])         , requestcode = 'foreman';  

my issue query above returns nothing. think it's doing it's finding highest datetime in submittime column not belong foreman request code.

how can return latest submittime specific request code?

i think can select this, if of course times don't repeat within requestcode:

select max(submittime)   [qtraxadmin].[qt_request]  requestcode = 'foreman';