Question

I have a table like:

userid    cityid
1         4
1         5
2         4
2         1
3         1
3         5

Is there a way in SQL or hive to transform it into a table like:

userid    city1    city4   city5
1         false    true    true
2         true     true    fase
3         true     false   true

I am not sure there is a word to describe this kind of operation…
Any help would be appreciated!

Answer 1

This is basically a PIVOT. You did not specify what RDBMS you are using but you can use an aggregate function and a CASE statement to get the results in any DB:

select userid,
  max(case when cityid = 1 then 'true' else 'false' end) city1,
  max(case when cityid = 2 then 'true' else 'false' end) city2,
  max(case when cityid = 3 then 'true' else 'false' end) city3,
  max(case when cityid = 4 then 'true' else 'false' end) city4,
  max(case when cityid = 5 then 'true' else 'false' end) city5
from yourtable
group by userid

See SQL Fiddle with Demo

Results:

| USERID | CITY1 | CITY2 | CITY3 | CITY4 | CITY5 |
--------------------------------------------------
|      1 | false | false | false |  true |  true |
|      2 |  true | false | false |  true | false |
|      3 |  true | false | false | false |  true |