Let's say I have a table with usernames:

Id  |  Name
-----------
1   |  Bobby
20  |  Bob
90  |  Bob
100 |  Joe-Bob
630 |  Bobberino
820 |  Bob Junior

I want to return a list of n matches on name for 'Bob' where the resulting set first contains exact matches followed by similar matches.

I thought something like this might work

SELECT TOP 4 a.* FROM
(
    SELECT * from Usernames WHERE Name = 'Bob'
    UNION
    SELECT * from Usernames WHERE Name LIKE '%Bob%'
) AS a

but there are two problems:

1. It's an inefficient query since the sub-select could return many rows (looking at the execution plan shows a join happening before top)
2. (Almost) more importantly, the exact match(es) will not appear first in the results since the resulting set appears to be ordered by primary key.

I am looking for a query that will return (for TOP 4)

Id | Name
---------
20 | Bob
90 | Bob

(and then 2 results from the LIKE query, e.g. 1 Bobby and 100 Joe-Bob)

Is this possible in a single query?