Does 'select distinct' returns the first distinct value or last distinct?

Question

When I query

select distinct Name from Emp;

Emp Table

ID   Name
1    Sam
2    Tom
3    Sam

does this query return first distinct name(with ID=1) from duplicate names or last distinct name(with ID=3)

How the distinct keyword actually works in this context?

Answer 1

I think there's a misunderstanding here: Your query does not return the records, only the distinct column values. Which, in your example, are 'Sam' and 'Tom'.

They have no particular order which can safely be expected. It may be the natural order, or the order in which they are processed on the database (completely depending on the database implementation), or semi-random (such as iterating over items in a set). The order may also vary depending on whether the result was retreived from the data or from the cache.

If you want a particular order, then specify it as order criterium:

select distinct Name from Emp order by Name asc

If you want the distinct values and the first record containing it, use group by:

select min(ID), Name from Emp group by Name