How To Get The Last Occurence Of Rows Containing Disticnt Value In One Column

I have a table that tracks GPS records broadly speaking as follows

tsDATETIME
usernameVARCHAR(16)
...
GPS data
...

I want to select the most recent GPS data for each distinct user.
That is, the table will have may records for a given username, but I
only want the most recent for each one.

For a single user I know I can do

SELECT TOP 1 * from <table> order by ts desc

But I want a set of results that effectively does this for
all users, and I can't work out the necessary query/subquery I
should be using.

I'm sure I'm missing something fairly obvious, so usual newbie
disclaimers apply.


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