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When you do not know the number of items that are to be concatenated beforehand, the code can become rather more demanding.The new features in SQL 2005 make some of the approaches easier.Quite often folks are confused about the potential of breaking relational fundamentals such as the First Normal Form or the scalar nature of typed values.(Talking about 1NF violations in a language like SQL which lacks sufficient domain support, allows NULLs and supports duplicates is somewhat ironic to begin with, but that is a topic which requires detailed explanations.) By ‘Concatenating row values’ we mean this: You have a table, view or result that looks like this……and you wish to have a resultset like the one below: In this example we are accessing the sample North Wind database and using the following SQL The objective is to return a resultset with two columns, one with the Category Identifier, and the other with a concatenated list of all the Product Names separated by a delimiting character: such as a comma.Concatenating column values or expressions from multiple rows are usually best done in a client side application language, since the string manipulation capabilities of Transact SQL and SQL based DBMSs are somewhat limited.However, you can do these using different approaches in Transact SQL, but it is best to avoid such methods in long-term solutions Even though SQL, in general, deviates considerably from the relational model, its reliance on certain core aspects of relational foundations makes SQL functional and powerful.Using common table expressions and the ROW_NUMBER() function, you can re-write this as: Note that ROW_NUMBER() is a newly-introduced feature in SQL 2005.If you are using any previous version, you will have to use the subquery approach (You can also use a self-join, to write it a bit differently).
In most cases, the requirement arises from the fact that there neither sufficient tools nor in-house expertise to develop tools that can extract the data as a resultset, and then massage the data in the desired display format.A simple, and intuitive way of displaying data is surprisingly difficult to achieve.Anith Sen gives a summary of different ways, and offers words of caution over the one you choose.If such an ordering criteria is not provided, the concatenated string would be arbitrary in nature.Generally, requests for row value concatenations often comes in two basic flavors, when the number of rows is known and small (typically less than 10) and when the number of rows is unknown and potentially large.
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The CASE in the recursive part of the CTE is used to eliminate the initial comma, but you can use RIGHT or the SUBSTRING functions instead.