SQL：选择 max(A), B 但不想分组或聚合 B

Question

If I have a house with multiple rooms, but I want the color of the most recently created, I would say:

select house.house_id, house.street_name, max(room.create_date), room.color
from house, room
where house.house_id = room.house_id
and house.house_id = 5
group by house.house_id, house.street_name

But I get the error:

Column 'room.color' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

If I say max(room.color), then sure, it will give me the max(color) along with the max(create_date), but I want the COLOR OF THE ROOM WITH THE MAX CREATE DATE.

just added the street_name because I do need to do the join, was just trying to simplify the query to clarify the question..

Answer 1

In standard SQL, you would write this as:

select r.house_id, r.create_date, r..color
from room r
where r.house_id = 5
order by r.create_date desc
offset 0 row fetch first 1 row only;

Note that the house table is not needed. If you did need columns from it, then you would use join / on syntax.

Not all databases support the standard offset / fetch clause. You might need to use limit , select top or something else depending on your database.

The above works in SQL Server, but is probably more commonly written as:

select top (1) r.house_id, r.create_date, r..color
from room r
where r.house_id = 5
order by r.create_date desc;

Answer 2

One option is WITH TIES and also best to use the explicit JOIN

If you want to see ties, change row_number() to dense_rank()

select top 1 with ties
       house.house_id
      ,room.create_date
      , room.color
from house
join room  on house.house_id = room.house_id
Where house.house_id = 5
Order by row_number() over (partition by house.house_ID order by room.create_date desc)

Answer 3

You could order by create_date and then select top 1:

select top 1 house.house_id, room.create_date, room.color
from house, room
where house.house_id = room.house_id
and house.house_id = 5
order by room.create_date desc

Answer 4

Expanding this to work for any number of houses (rather than only working for exactly one house)...

SELECT
  house.*,
  room.*
FROM
  house
OUTER APPLY
(
  SELECT TOP (1) room.create_date, room.color
    FROM room
   WHERE house.house_id = room.house_id
ORDER BY room.create_date DESC
)
  AS room