If i use a table containing at least 2 columns like this :
SELECT * USER WHERE LastName = 'Dupont' AND FirstName = 'Robert'
SELECT * USER WHERE FirstName = 'Robert' AND LastName = 'Dupont'
The order of the comparisons does not matter. SQL Server should optimize the
WHERE clause for the data.
However, if you care about performance, you should use an index, either
user(firstname, lastname) or
user(lastname, firstname). The order of comparisons is not the right thing to be thinking about.