How Do I convert this table from row to column? - mysql

Question

I have a table that contains id and country name, and I need to convert them so the id with more than 1 country will display in 1 row.I have been searching in this forum for over an hour and found nothing.
I tried if using the pivot function can help me to achieve the result i wanted, but I feel like using pivot does not work on my case here.
This is a mini version of the table I have. The number of distinct value in the field "country" will be over 100, so I can just say something like when county = '..' as this will be to repetitive.
enter code here
+----+--------+
| id | country|
+----+--------+
| 1 | US |
| 1 | UK |
| 2 | JP |
+----+--------+
Desired outcome I am looking for:
enter code here
+----+-----------+-----------+
| id | country_1 | country_2 |
+----+-----------+-----------+
| 1 | US | UK |
| 2 | JP | null |
+----+-----------+-----------+
I found this question which is similar but it is the opposite of what I am trying to achieve.
MySQL statement to pivot table without using pivot function or a union
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update:
Thank you so much for all of your helps. I may not have used the queries of yours to solve my problem - as of the fact that the syntax is a bit diff running in snowflake. However, I got the insights I need from all of you.
here is my solution:
enter code here
select t1.id,
max(iff(t1.row_number = 1, t1.country ,null)) as country_1,
max(iff(t1.row_number = 2, t1.country ,null)) as country_2,
max(iff(t1.row_number = 3, t1.country, null)) as country_3
from
(
select id, country, row_number() over (partition by id order by id ) as
row_number
from table
) t1
group by t1.id

Answer 1

Whereas you could do it with "pivoting", what will happen when you have 3 countries? Or 4? Or 17?
May I suggest this:
SELECT id,
GROUP_CONCAT(country)
FROM tbl
GROUP BY id;
You will get something like:
1 US,UK
2 JP

Answer 2

use aggregation
select id, max(case when id=1 then country end ) as country_1,
max(case when id=2 then country end ) as country_2
from tbale group by id

Answer 3

As you comment on #Rick answer you have max 3 country for each id then you can use this
select
id,
(select country from test where test.id=t.id limit 0,1)as country_1,
(select country from test where test.id=t.id limit 1,1)as country_2,
(select country from test where test.id=t.id limit 2,1)as country_3
from test as t
group by id;
DEMO

Answer 4

You can try this following script with RowNumber generated per id. As you confirmed there are maximum 3 country per id, we can easily generate your desired result set by handling RowNumber 1,2 & 3
SELECT ID,
MAX(CASE WHEN RowNumber = 1 THEN country ELSE NULL END) Country_1,
MAX(CASE WHEN RowNumber = 2 THEN country ELSE NULL END) Country_2,
MAX(CASE WHEN RowNumber = 3 THEN country ELSE NULL END) Country_3
FROM
(
SELECT id,
country,
#row_num :=IF(#prev_value = concat_ws('',id),#row_num+1,1)AS RowNumber
,#prev_value := concat_ws('',id)
FROM tbale
ORDER BY id
)A
GROUP BY id

Answer 5

There's no "dynamic" PIVOT in SQL. You need to specify the list of columns when writing the query. Your options are:
If you know the number of columns in advance, then #ZaynulAbadinTuhin solution is the easier. It seems, however, this is not your case.
If you don't know the number of columns in advance and you want them all concatenated in a single column, then #Rick James solution is the best.
Otherwise, you can still use some kind of dynamic SQL in your app or in a stored procedure that will build the SQL query at runtime, based on the existing values of the table. But this solution would require much more programming. It's not a single/simple SQL query anymore. See Rick James's Pivoting in MySQL stored procedure.