Question

Suppose I have a set in SQL like this:

    Product | Quantity
       A         1
       B         2

I want (in a single SELECT statement) to transform that to:

    Product 
       A    
       B    
       B

Can anyone point me towards (T-SQL preferably), a trick on how to do this?

Answer 1

You need an intermediary numbers table, or a table-valued function (if that option is available to you) which will produce numbers.

Assuming you had a Numbers table, which is populated like so:

    Number
    ------
         1
         2
       ...
    100000

(or as large as you need it to be, and there are efficient mechanisms for generating a numbers table of large size)

You would then issue the following query:

select
    p.Product
from
    Products as p
        inner join Numbers as n on n.Number <= p.Quantity 

This would produce the result you want.

A numbers table is incredibly helpful in SQL, and Itzik Ben-Gan goes into it and other great querying techniques in his books (listed on his website). I highly recommend them.