mysql - SQL SELECT to get the first N positive integers

Question

I need to get a result set containing the first N positive integers. Is it possible to use only standard SQL SELECT statement to get them (without any count table provided)?

If it's not possible, is there any specific MySQL way to achieve this?

Answer 1

Seems that what you want is a dummy rowset.

In MySQL, it's impossible without having a table.

Most major systems provide a way to do it:

• In Oracle:

  SELECT  level
  FROM    dual
  CONNECT BY
          level <= 10
  

• In SQL Server:

  WITH    q AS
          (
          SELECT  1 AS num
          UNION ALL
          SELECT  num + 1
          FROM    q
          WHERE   num < 10
          )
  SELECT  *
  FROM    q
  

• In PostgreSQL:

  SELECT  num
  FROM    generate_series(1, 10) num
  

MySQL lacks something like this and this is a serious drawback.

I wrote a simple script to generate test data for the sample tables in my blog posts, maybe it will be of use:

CREATE TABLE filler (
        id INT NOT NULL PRIMARY KEY AUTO_INCREMENT
) ENGINE=Memory;

CREATE PROCEDURE prc_filler(cnt INT)
BEGIN
        DECLARE _cnt INT;
        SET _cnt = 1;
        WHILE _cnt <= cnt DO
                INSERT
                INTO    filler
                SELECT  _cnt;
                SET _cnt = _cnt + 1;
        END WHILE;
END
$$

You call the procedure and the table gets filled with the numbers.

You can reuse it during the duration of the session.