How to Concatenate Labels Based on Response ID Using SQL?

Concatenating Values Based on ID: A Solution Using SQL

When working with data, the need to concatenate values based on shared IDs arises frequently. In this scenario, we encounter a table with a list of Response IDs and associated Labels. Our goal is to transform this data into a format where each row displays the Response ID and a comma-separated list of Labels.

To achieve this, we can leverage SQL's grouping and concatenation capabilities. We begin by declaring a temporary table called @T and populating it with the sample data. The query below outlines the steps involved:

select T1.Response_ID,
       stuff((select ','+T2.Label
              from @T as T2
              where T1.Response_ID = T2.Response_ID
              for xml path(''), type).value('.', 'varchar(max)'), 1, 1, '') as Label
from @T as T1
group by T1.Response_ID

1. Grouping: We group the data by the Response_ID using the group by T1.Response_ID clause. This step ensures that we operate on a single set of Labels for each Response ID.
2. Subquery: Within each group, we use a subquery to retrieve the Labels associated with that Response ID. The subquery retrieves the Label values and combines them into a single string separated by commas. The .value('.', 'varchar(max)') part handles cases where Labels contain XML-unfriendly characters.
3. Concatenation: The stuff() function is employed to concatenate the comma-separated Labels into a single string. It removes the leading comma by specifying 1, 1, '' as the removal arguments.
4. Projection: Finally, the select statement projects the Response_ID and the concatenated Label column as the desired output.

By executing this query, we obtain the transformed data where each row represents a Response ID with the associated Labels concatenated and separated by commas. This solution provides an efficient way to aggregate and present data based on shared identifiers.

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