Question

I was having a look at this question: Getting random value from a SQLite table and it got me wondering if one can duplicate records using SQL. More specifically, is there a construct that allows to transform these records:

id| name| count
---------------
 1| Anne|     3
 2|  Joe|     2

into:

id| name
--------
 1| Anne
 1| Anne
 1| Anne
 2|  Joe
 2|  Joe

where the count of Anne and Joe records in the latter matches the corresponding count value in the former set of records.

Can it be done with SQL? If so, how?

EDIT:

Lucero asks what SQL dialect; any really, but ideally the most agnostic approach would be the best.

ANOTHER EDIT:

Can it be done within a single SQL statement in say sqlite?

Answer 1

You can use a “numbers” table (it’s handy for various operations):

CREATE TABLE num
( i UNSIGNED INT NOT NULL
, PRIMARY KEY (i)
) ;

INSERT INTO num (i)
VALUES
  (1), (2), ..., (1000000) ;

Then:

SELECT 
    t.id, t.name
FROM 
        tableX AS t
    JOIN
        num
            ON num.i <= t."count"

Warning: There is of course a limitation on this approach. The query will not produce all the wanted rows, as soon as you have a value in the count column that exceeds the maximum value stored in the Numbers table. If the values in the count column are unbounded, then only an iterative or recursive solution (like the other two answers) can work.