Find the most frequent data every year in SQL - sql

Question

TableA :
Years Data
2000 A
2000 B
2000 C
2000 C
2000 D
2001 A
2001 B
2001 B
2002 B
2002 D
2002 D
I want to output:
Years Data
2000 C
2001 B
2002 D
My solution:
SELECT DISTINCT Years, Data
FROM
(
SELECT Years, Data, COUNT(*) AS _count
FROM TableA
GROUP BY Years, Data
) a1
ORDER BY Years, _count DESC
But it have a problem:
ORDER BY items must appear in the select list if SELECT DISTINCT is specified.
How do I correct my SQL code?

Answer 1

Assuming your database supports row_number(), you can do it like this:
SELECT Years, Data
FROM
(
SELECT Years,
Data,
ROW_NUMBER() OVER(PARTITION BY Years ORDER BY count(*) DESC) rn
FROM TableA
GROUP BY Years, Data
) x
WHERE rn = 1
ORDER BY Years, Data
See a live demo on rextester.

Answer 2

Try this:
select t.Years, t.[Data]
from (
select *, count(*) cnt
from TableA
group by years, [Data]
) t
left join (
select Years, max(cnt) maxCnt
from (
select *, count(*) cnt
from TableA
group by years, [Data]
) t
group by Years
) tt on t.Years = tt.Years -- tt is a view that gives you max count of each year
where t.cnt = tt.maxCnt -- you need `years`, `[Data]` that its count is max count
order by years;
SQL Fiddle Demo
Another way is to use rank() in a DBMS that supports it:
;with t as (
select *, count(*) cnt
from TableA
group by years, [Data]
), tt as (
select *, rank() over (partition by years order by cnt desc) rn
from t
)
select years, [Data]
from tt
where rn = 1
order by years;
SQL Fiddle Demo

Answer 3

If you're using oracle, you can use the function STATS_MODE
select years, stats_mode(data)
from tablet
group by years;
https://docs.oracle.com/cd/B19306_01/server.102/b14200/functions154.htm

Answer 4

Your error is "ORDER BY items must appear in the select list if SELECT DISTINCT is specified."
This means you have put something in the ORDER BY that is not in the SELECT. In this case, _count DESC is not in the SELECT statement
SELECT DISTINCT Years, Data, _count DESC
FROM
(
SELECT Years, Data, COUNT(*) AS _count
FROM TableA
GROUP BY Years, Data
) a1
ORDER BY Years, _count DESC