Tuesday, 18 January 2011

Repeating a SQL row based on a value in a different column

There are times that we get requirements such as populating and duplicate SQL rows, based on a value, on another column. E.g.: In an inventory system when items are received those details will be saved in the following format (ItemDetails) :

screen_01

And we are asked to create a GUI for end user to enter ‘Serial Numbers’ for each item. And we have to repeat the above mentioned item codes number of times which equals to the ‘ItemQty’. Of course we can achieve that using a SQL cursor or iterate using C# coding. But following example I will show how to do it using SQL.

The task would have been very simple if we would have a another table with a structure similar to this: (TempTable)

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So when the two table are joined ‘ItemDetails’ will repeat according to the row count of the ‘TempTable’. But it is not very practical, and it will result in duplicating data, which will grow your database un-necessary when time goes.

But instead we can use on single table which contains a series of numbers. These numbers will start from ‘1’. And the end should be the maximum quantity which an Item can have. For this example I will take ‘10’ as the maximum value. And that table should have the following structure.

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Use the following T-SQL statement to create the table:

CREATE TABLE [IntermediateTable](
[MaxQty] [int] NULL
) ON [PRIMARY]


For this example I have inserted up to 20. But in a real world scenario it may be required to enter values (More than 1000). In a similar situation you can use the following T-SQL statement to insert values.


insert into IntermediateTable
select
thousand.number*1000 +
hundred.number*100 +
ten.number*10 +
one.number
from(
select 1 as number union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9 union select 0) one
cross join (select 1 as number union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9 union select 0) ten
cross join (select 1 as number union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9 union select 0) hundred
cross join (select 1 as number union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9 union select 0) thousand
where (thousand.number*1000 + hundred.number*100 + ten.number*10 + one.number) > 0 and (thousand.number*1000 + hundred.number*100 + ten.number*10 + one.number) <= 2000
order by (thousand.number*1000 + hundred.number*100 + ten.number*10 + one.number)



** Please Note : Above statement will insert values from ‘1’ to ‘2000’. But removing the where condition will insert values from ‘0’ to ‘10000’.


And using the following T-SQL statement we can join the table and produce the required result.


select A.*
from ItemDetails as A
join IntermediateTable as B on B.MaxQty <= A.ItemQty
where A.BatchNo = 'B1'


screen_04

3 comments:

  1. more easy way to generate a numbers table:

    CREATE TABLE dbo.Numbers
    (
    Number INT IDENTITY(1,1) PRIMARY KEY CLUSTERED
    )

    WHILE COALESCE(SCOPE_IDENTITY(), 0) <= 1024
    BEGIN
    INSERT dbo.Numbers DEFAULT VALUES
    END

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