Wednesday, 24 October 2012

Generating Unique Values Against a New Dataset

non-SQL developers look away now....

Here's another Data Analysis tip...

When dealing with brand new datasets a DBA Developer sometimes needs to add a unique value which will form a way of identifying each row. The ROW_NUMBER() function is an obvious choice but if the data contains duplicates or has data quality issues it can be tricky. This method doesn't rely on the data itself, it just adds the unique values you need.

First we add a column that will contain the incremental number......

-- add a new column called rownum
alter table test_data add rownum int

Now we run the following three line script......

-- declare a variable that be used to assign incremental numbers
declare @i int
--assign a starting point for our id's

select @i = 10000000
-- The update statement will populate the column 
-- with consecutive numbers starting with 10000001
update test_data set @i = rownum = @i +1

I used 10000000 as a starting point so that each number will be the same length and will appear consistent when used in a reporting scenario and when exported back out to tools such as Microsoft Excel. 

One to have in your SQL tool kit for sure.....Enjoy!

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