pass pure time to my query

I have a datetime field which contains data like following:

03:15:00 PM
04:25:00 PM

I have a query and would like to query on this field like following:

Select myfield from mytable where mydatetime = @MyDateTime

I pass '03:15:00 PM' to the function.
For some reason, it does not return the record.
I tried to use convert(char(15), @MyDateTime, 108) which does not work
and tried to use cast which does not work either.

I would like to know how I can query a datetime field for pure time
information,
Your help is great appreciated,

A datetime value represents an instant in history. This is a date plus a time. Today at 3:15:00 PM is a different datetime than tomorrow at 3:15:00 PM.

When you feed the string '03:15:00 PM' to a query that wants to compare it to a datetime, it will convert the string to a datetime first ... and that string will represent the time 3:15:00 PM *ON THE DATE 1/1/1900*.

Comparing that datetime to any datetime in your table is unlikely to find a match, unless you have dates in your table from the early 20th century.

You need to either compare the string to the time format of the original datetime --

Select myfield from mytable where convert(char(15), mydatetime, 108) = convert(char(15), @MyDateTime, 108)

or use other methods of matching the time:

-- this expresses datetimes as doubles, then throws away the integer part of it,
-- which represents the date; leaving a double between zero and one that
-- expresses the time
Select myfield from mytable
where convert(double, mydatetime) - floor(convert(double, mydatetime))
= convert(double, @mydatetime) - floor(convert(double, mydatetime))

-- this computes the number of seconds since a reference point,
-- then subtracts (the number of days since that reference point) * 86400
Select myfield from mytable
where datediff(second, mydatetime, '2000-01-01') - datediff(day, mydatetime, '2000-01-01')*86400
= datediff(second, @mydatetime, '1900-01-01')