selecting data from a column and display them in different columns based on their values

Question

I'm trying to select a value from a table like the following example:

user   id
----------
a       1
b       1
c       3
d       2
a       3

and the result will be like the following:

user  id_1  id_2  id_3
-----------------------
a      1     NULL   3
b      1     NULL   NULL
c      NULL  NULL   3
d      NULL  2      NULL

so basically what I'm trying to accomplish is to get all the users with id's ==1 to a column and the users with id ==2 to another column and users with id ==3 to a third column and the users are duplicated like the case for user 'a' when it showed once with id=1 and id=3 and I want to capture this duplication in the resulting table.

Any idea would be appreciated. Thanks in advance!

Answer 1

This is called a pivot. You can do this with conditional aggregation:

select user,
       max(case when id = 1 then id end) as id_1,
       max(case when id = 2 then id end) as id_2,
       max(case when id = 3 then id end) as id_3
from table t
group by user
order by user;