Distinct with order by clause - sql

Question

I want to get distinct Category and order there result by curdate column.
select distinct(Category)'Category' from sizes order by curdate desc
But this simple query is generating errors.
ORDER BY items must appear in the select list if SELECT DISTINCT is specified.

Answer 1

I'm afraid you have the same constraint for SELECT DISTINCT as for GROUP BY clauses: namely, you cannot make use of a field that's not declared in the fields list, because it simply doesn't know which curdate to use when sorting in case there are several rows with different curdate values for the same Category.
EDIT: try something like:
SELECT Category FROM sizes GROUP BY Category ORDER BY MAX(curdate) DESC
Replace MAX with MIN or whatever suits you.
EDIT2: In this case, MAX(curdate) doesn't even have to be present in the field list since it's used in an aggregate function.

Answer 2

with cte as
(
select
Category,
[CurDate],
row_number() over(partition by Category order by [CurDate]) as rn
from sizes
)
select
Category
from cte
where rn = 1
order by [CurDate]

Answer 3

You look to be after a list of all the categories, with a date associated with each one. Whether you want the earliest first or latest first, you should be able to do one of the following:
SELECT Category, MAX(curdate) FROM sizes GROUP BY Category
Or:
SELECT Category, MIN(curdate) FROM sizes GROUP BY Category
Depending on whether you want the most recent or earliest dates associated with each category. If you need the list to then be ORDERed by the dates, add one of the following onto the end:
ORDER BY MAX(curdate)
ORDER BY MIN(curdate)

Answer 4

Curdate must be in your select statement also, right now you are only specifying Category

Answer 5

Exactly what the error says, it cannot order a distinct list if the sort filed is not part of the select. Reason being is that there may be multiple sort values for each of the distinct values selected. If the data looks like this
Category CurDate
AAA 1/1/2011
BBB 2/1/2011
AAA 3/1/2011
Should AA be before or after BBB in the distinct list? If you just ordered by the date without the distinct you would get it in both positions. Since SQL doesn't know which date should be associated with the distinct category it will not let you sort by the date.

Answer 6

as the error-message said, you can't order by a column that isn't selected wehen using SELECT DISTINCT (same problem as with GROUP BY...). change your query to this:
SELECT DISTINCT category, curdate FROM sizes ORDER BY curdate DESC
EDIT: replying to yourt comment:
if you want to select the distinct category with the last date for every category, you'll have to change your query a bit. i can think of two possibilities for this: using MAX() like Costi Ciudatu posted or doing some crazy stuff with subselects - the first one would be the better approach.