Duplicating rows in one select MySql query

Question

At first I would like greet all Users and apologize for my english :). I'm new user on this forum. I have a question about MySQL queries. I have table Items with let say 2 columns for example itemsID and ItemsQty.

itemsID ItemsQty
11  2
12  3
13  3
15  5
16  1

I need select itemsID but duplicated as many times as indicated in column ItemsQty.

itemsID ItemsQty
11  2
11  2
12  3
12  3
12  3
13  3
13  3
13  3
15  5
15  5
15  5
15  5
15  5
16  1

I tried that query:

SELECT items.itemsID, items.itemsQty

FROM base.items 

LEFT OUTER JOIN 
(

  SELECT items.itemsQty AS Qty FROM base.items

) AS Numbers ON items.itemsQty <=Numbers.Qty

ORDER BY items.itemsID; 

but it doesn't work correctly. Thanks in advance for help.

Answer 1

SQL answer - Option 1

You need another table called numbers with the numbers 1 up to the maximum for ItemsQuantity

Table: NUMBERS

1
2
3
4
5
......
max number for ItemsQuantity

Then the following SELECT statement will work

SELECT ItemsID, ItemsQty
FROM originaltable
JOIN numbers
    ON originaltable.ItemsQty >= numbers.number
ORDER BY ItemsID, number

See this fiddle -> you should always set-up a fiddle like this when you can - it makes everyone's life easier!!!

code answer - option 2

MySQL probably won't do what you want 'cleanly' without a second table (although some clever person might know how)

What is wrong with doing it with script?

Just run a SELECT itemsID, ItemsQty FROM table

Then when looping through the result just do (pseudo code as no language specified)

newArray = array();  // new array

While Rows Returned from database{ //loop all rows returned

    loop number of times in column 'ItemsQty'{

          newArray -> add 'ItemsID'


    }


}//end of while loop

This will give you a new array

0 => 11

1 => 11

2 => 12

3 => 12

4 => 12

5 => 13

etc.

Answer 2

Select DISTINCT items.itemsID, items.itemsQty From base.items left outer join (select items.itemsQty as Qty from base.items) As Numbers On items.itemsQty <=Numbers.Qty  
order by items.itemsID;

Use DISTINCT to remove duplicates. Read more here - http://dev.mysql.com/doc/refman/5.0/en/select.html

Answer 3

It seems like I understood what you asked differently than everyone else so I hope I answer you question. What I would basically do is -

1. create a new table for those changes.
2. Create a mysql procedure which given a line in the original table add new lines to the new table - http://dev.mysql.com/doc/refman/5.6/en/loop.html
3. Run this procedure for each line in the original table.

Answer 4

try this to get distinct values from both columns

SELECT DISTINCT itemsID FROM items
UNION 
SELECT DISTINCT itemsQty FROM items