如何在Oracle SQL中使用MAX（）和COUNT（）？

Question

Suppose i have the following table:

transactions(id, type)

id - id of the costumer (integer 1...n)
type - what they bought (like "apple")

Note that each row refers to buying only ONE of the given type.

How can I select the id of the costumer who bought the most of a given type (like apple)?

I tried to COUNT() the rows where type = apple for each id, but I cannot use MAX() in that query to select only the first ID.

Thanks

Answer 1

You can first make a query that for every customer counts the amount of times he bought an 'apple' , with:

SELECT id,COUNT(*) AS total
FROM transactions
WHERE type = 'apple'
GROUP BY id

Now we only need to ORDER BY that total in DESC ending order, and return the first row with FETCH FIRST n ROWS ONLY , like:

SELECT id,COUNT(*) AS total
FROM transactions
WHERE type = 'apple'
GROUP BY id

Answer 2

This is SQL 101, you should read about group by clause:

select id,
    count(*) as count_of_apples
from transactions
where type = 'apple'
group by id
order by count(*) desc

Answer 3

As you are asking for Oracle in particular: STATS_MODE gives you the value that occurs most often.

select stats_mode(id)
from transactions
where type = 'apple';