Add multiple rows in a single row with different columns

Question

I want to join two tables (they are called Registers and Reads). As a result I would like to obtain 4 columns, corresponding to Registers ID.

According to the next example, by joining the tables, I obtain 2 rows. There could be some cases that I may find/obtain 4 rows because they exist in Reads table.

Table: Registers

    ID      Number    Prod_ID
    331       01       112233
    332       02       112233
    333       03       112233
    334       04       112233

Table: Reads

    Read_Id    Register_Id  
      011          331
      012          332

I use this query to link join both tables:

    SELECT rg.ID 
    FROM Reads rd LEFT JOIN Registers rg on rd.Register_ID = rg.ID
    WHERE rg.Prod_ID = 112233;

My result is next one:

    ID
    331
    332

What I really want is to obtain just one row, assigning the first result to the first column, second one to the second and so on. In addition, I would like to add an extra column that shows how many columns contain information.

Expected result:

    RegisterID1    RegisterID2    RegisterID3    RegisterID4    Count
        331            332                                        2

Is there any easy way to do this? Thank you very much!

Answer 1

You are on 10g, so PIVOT is unavailable, but still have the good old sum(case ...).

drop table reads purge;
drop table registers purge;

create table registers (id number,  n varchar2(2), prod_id number);
insert into registers values (331, '01', 112233);
insert into registers values (332, '02', 112233);
insert into registers values (333, '03', 112233);
insert into registers values (334, '04', 112233);
commit;

create table reads (read_id varchar2(3), register_id number);
insert into reads values ('011', 331);
insert into reads values ('012', 332);
commit;

SELECT
  sum(case when rg.n = '01' then rd.register_id end) as "RegisterID1",
  sum(case when rg.n = '02' then rd.register_id end) as "RegisterID2",
  sum(case when rg.n = '03' then rd.register_id end) as "RegisterID3",
  sum(case when rg.n = '04' then rd.register_id end) as "RegisterID4",
  count(rd.register_id) as "Count"
FROM Reads rd RIGHT JOIN Registers rg on rd.Register_ID = rg.ID
WHERE rg.Prod_ID = 112233;

RegisterID1 RegisterID2 RegisterID3 RegisterID4      Count
----------- ----------- ----------- ----------- ----------
        331         332                                  2

Answer 2

Balazs Papp's solution works perfectly. I have edited my next question, which shows the tables (create, instert...)

I would like to add a new field to the table: date_reading

Read_Id    Register_Id      Date
  011          331       14-Apr-2018
  012          332       21-Apr-2018

The result I want would be the next one:

RgstrID1 |  D1       |RgstrID2  |  D2       |RgistrID3|D3|RgistrID4|D4|Count
    331  |14-Apr-2018|     332  |21-Apr-2018|         |  |         |  |  2

Tables would be

create table registers (id number,  n varchar2(2), prod_id number);
insert into registers values (331, '01', 112233);
insert into registers values (332, '02', 112233);
insert into registers values (333, '03', 112233);
insert into registers values (334, '04', 112233);

create table reads (read_id varchar2(3), register_id number, Date_time timestamp);
insert into reads values ('011', 331, '14-Apr-2018');
insert into reads values ('012', 332, '21-Apr-2018');

Is it possible to do it?

Here there is the Fiddle link