MySQL Select rows on first occurrence of each unique value

Question

Let\'s say you have the following table (the column of interest here is cid):

+-----+-------+-------+-------+---------------------+-------------         


        

Answer 1

mysql has a "cheat" for this:

select *
from mytable
group by cid;

That's all you need, because in mysql it allows you to not aggregate the non-grouped-by columns (other databases would throw a syntax error), in which case it outputs only the first occurrence of each group-by value(s). Note though that this won't guarantee the way in which the "first" occurrence is determined (it will be just how the rows are read in)

If you want a particular first occurrence, sort first, then apply the group-by cheat:

select *
from (
    -- order by the "time" column descending to get the "most recent" row
    select * from mytable order by time desc
    ) x
group by cid