SQL Query to return N rows from dual

Question

I want to write a SQL query which accepts a bind variable (say :NUM) and its output consists of one column & :NUM number of rows, each row having its row number. i.e. if we

Answer 1

I didn't come up with this answer [ so make sure any votes go the right way!!] , it just my testing notes based on 'OMG Ponies' [who wasn't sure whether the method would work with binding variable] above for reference:

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options

SQL> var num_rows number
SQL> begin select 20 into :num_rows from dual;
  2  end;
  3  /

PL/SQL procedure successfully completed.

SQL> select level from dual
  2  connect by level <=:num_rows;

     LEVEL
----------
         1
         2
         3
         4
 ...

Answer 2

WITH cte_numbers(n) 
AS (
    SELECT 0
    UNION  ALL
    SELECT n + 1
    FROM  cte_numbers
    WHERE n < 10
)
SELECT n
FROM cte_numbers;

Returned Rows 0 1 2 3 4 5 6 7 8 9 10

Answer 3

Another way is to use an XQuery range expression, e.g.:

select column_value from xmltable(:a||' to '||:b);

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10

This solution is quite flexible, e.g.:

select column_value from xmltable('5 to 10, 15 to 20');

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10
15
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20

Answer 4

Try something like:

SELECT 1 AS Val FROM dual
UNION ALL SELECT 2 FROM dual
UNION ALL SELECT 3 FROM dual
UNION ALL SELECT 4 FROM dual
UNION ALL SELECT 5 FROM dual
UNION ALL SELECT 6 FROM dual
UNION ALL SELECT 7 FROM dual;

It's messy, but it'll do the trick.

Edited: Ah - you need to pass in a variable to let you know how high to go...

So how about something like:

SELECT t1.Val + t2.Val * 2 + t3.Val * 4 + t4.Val * 8 AS Val
FROM
(
SELECT 0 AS Val FROM dual
UNION ALL SELECT 1 FROM dual
) AS t1, 
(
SELECT 0 AS Val FROM dual
UNION ALL SELECT 1 FROM dual
) AS t2, 
(
SELECT 0 AS Val FROM dual
UNION ALL SELECT 1 FROM dual
) AS t3, 
(
SELECT 0 AS Val FROM dual
UNION ALL SELECT 1 FROM dual
) AS t4
WHERE t1.Val + t2.Val * 2 + t3.Val * 4 + t4.Val * 8 <= 7;

Ok... editing again, now using WITH:

WiTH 
A0 AS (SELECT 0 as N FROM DUAL UNION ALL SELECT 0 FROM DUAL),
A1 AS (SELECT 0 as N FROM A0, A0 AS B),
A2 AS (SELECT 0 as N FROM A1, A1 AS B),
A3 AS (SELECT 0 as N FROM A2, A2 AS B),
A4 AS (SELECT 0 as N FROM A3, A3 AS B),
A5 AS (SELECT 0 as N FROM A4, A4 AS B),
A6 AS (SELECT 0 as N FROM A5, A5 AS B),
Nums AS (SELECT ROW_NUMBER() OVER (ORDER BY N) AS Val FROM A6)
SELECT *
FROM Nums
WHERE Val <= :NUM
;

Answer 5

I'm marking this community wiki since it doesn't actually answer your requirement for no tables, but one of the first things we do when installing a database is to create a set of tables for this sort of purpose.

• A table containing a large number of integers (e.g., -99999 through 99999).
• A table containing every date from 10 years in the past to 10 years in the future (which is continuously added to each month and trimmed occasionally).
• A table containing each hour of the day.

By doing this, we greatly reduce the complexity, and increase the speed, of a large number of our queries at the cost of (minimal and cheap) disk space.

You should give some serious thought to that. Aside from maintaining the date table, there's not a lot of upkeep needed.

Answer 6

Another solution would require some PL/SQL to create a function to return a collection with the rows... Not as simple as the select level from dual connect by level <= :b1 approach, but it's useful in a few situations:

1) Create a number table object type ( number_tbl, in this example ) :

create or replace type number_tbl as table of number;

2) Create a function that will receive the number of rows to be generated, and then return a number_tbl object with the results:

create or replace function get_rows( i_num_rows number ) return number_tbl as
  t number_tbl := number_tbl();
begin
  if i_num_rows < 1 then
    return null;
  end if;

  t.extend( i_num_rows );

  for i in 1..i_num_rows loop
    t(i) := i;
  end loop;

  return t;
end get_rows;

3) select from your function using the table( ... ) function to turn your number_tbl object into something selectable:

select * from table( cast ( get_rows( :b1 ) as number_tbl ) );