postgreSQL-从许多列中获得最频繁的值

Question

I have a table hobbies:

+++++++++++++++++++++++++++++++
+ hobby_1 | hobby_2 | hobby_3 +
+---------+---------+---------+
+ music   | soccer  | [null]  +
+ movies  | music   | cars    +
+ cats    | dogs    | music   +
+++++++++++++++++++++++++++++++

I want to get to most freuqent used value. The answer would be music

I know the query to get the most frequent value for one column:

SELECT hobby_1, COUNT(*) FROM hobbies
    GROUP BY hobby_1
    ORDER BY count(*) DESC;

But how to get the most frequent value when combining all columns.

Answer 1

You need to unpivot the data. Here is one method:

select h.hobby, count(*)
from ((select hobby_1 as hobby from hobbies) union all
      (select hobby_2 as hobby from hobbies) union all
      (select hobby_3 as hobby from hobbies) 
     ) h
group by h.hobby
order by count(*) desc;

However, you should really fix your data structure. Having multiple columns only distinguished by a number is usually a sign of a problem with the data structure. You should have a table with one row for each hobby.