选择以获得1列的两个不同查询结果作为2列的一个结果

Question

I have the two queries which are mostly simple select statements which are in no way related to each other but both returning same number of rows.

SQL> select first_name from employees where rownum <=3;
FIRST_NAME
--------------------
Ellen
Sundar
Mozhe

SQL> select department_name from departments  where rownum <=3;

DEPARTMENT_NAME
------------------------------
Administration
Marketing
Purchasing

I want the result of both the sqls as the result of 1 select query returning the values of two select statements as 1 result with 2 columns (one for each select statement)

FIRST_NAME      DEPARTMENT_NAME
--------------  ------------------
Ellen           Administration
Sundar          Marketing
Mozhe           Purchasing

Here is what i tried, but i get duplicates in results

select first_name, department_name from 
(select first_name from employees where rownum <=5),
(select department_name from departments  where rownum <=5);

or

with q1 as (select first_name from employees where rownum <=5),
q2 as (select department_name from departments  where rownum <=5)
select first_name, department_name from q1, q2;

which gives

FIRST_NAME           DEPARTMENT_NAME
-------------------- -------------------
Ellen                Administration
Sundar               Administration
Mozhe                Administration
David                Administration
Hermann              Administration
Ellen                Marketing
Sundar               Marketing
Mozhe                Marketing
David                Marketing
Hermann              Marketing
Ellen                Purchasing
Sundar               Purchasing
Mozhe                Purchasing
David                Purchasing
Hermann              Purchasing
Ellen                Human Resources
Sundar               Human Resources
Mozhe                Human Resources
David                Human Resources
Hermann              Human Resources
Ellen                Shipping
Sundar               Shipping
Mozhe                Shipping
David                Shipping
Hermann              Shipping

Please Help.

Answer 1

You can do:

WITH indexed_employees AS (
  SELECT rownum AS idx,
         first_name
  FROM   employees
  WHERE  rownum <=3
),
indexed_departments AS (
  SELECT rownum AS idx,
         department_name
  FROM   departments
  WHERE  rownum <=3
)
SELECT e.first_name,
       d.department_name
FROM   indexed_employees e
       INNER JOIN
       indexed_departments d
       ON( e.idx = d.idx )
ORDER BY e.idx

However, this does not make much syntatic sense to link the two fields in this way as they are not related.

If you are just trying to reduce the number of round trips to the database, you could instead use a stored procedure which returns two cursors (one for each query).

CREATE PROCEDURE get_Top_Emps_and_Depts(
   out_employees_cursor     OUT SYS_REFCURSOR,
   out_departments_cursor   OUT SYS_REFCURSOR
)
AS
BEGIN
  OPEN out_employees_cursor FOR
  SELECT first_name
  FROM   employees
  WHERE  rownum <=3;

  OPEN out_departments_cursor FOR
  SELECT department_name
  FROM   departments
  WHERE  rownum <=3;
END get_Top_Emps_and_Depts;
/

Answer 2

You have to enumerate rows at first somehow, for instance with rownum and then join them using that key:

with q1 as (select rownum rn, first_name from employees where rownum <=5),
q2 as (select rownum rn, department_name from departments where rownum <=5)
select first_name, department_name from q1 join q2 using (rn);