For the order by clause

order by clause specifies the sort order

select username from user order by username;

Sort basis for finding out the username username alphabetical order, the default is ascending (AZ)

Can also be carried out in descending order, you must specify the DESC keyword

In the above sql statement becomes

select username from user order by username desc;

It will become in descending order.

For multiple filter criteria clause, usually first the first condition, if the same as the first, only to compare the second.