How to Concatenate Strings Within a SQL Server GROUP BY Using FOR XML PATH?

The clever combination of SQL Server string concatenation and GROUP BY

In SQL Server, there is a clever way to combine FOR XML and PATH to concatenate strings in a GROUP BY operation.

The goal is to convert the following data:

<code>id       Name       Value
1          A          4
1          B          8
2          C          9</code>

Convert to:

<code>id          Column
1          A:4, B:8
2          C:9</code>

The steps are as follows:

1. Create temporary table: Create a temporary table with the same schema as the original table.

2. Insert sample data: Insert sample data into a temporary table.

3. Concatenate strings using FOR XML and PATH: Concatenate strings within each ID group using the FOR XML and PATH methods. This includes:

   • Select the ID and Name columns.
   • Use a subquery to retrieve Name and Value for each record in the same ID group.
   • Join the , and Name columns using a delimiter (for example, Value).
   • Use FOR XML PATH('') to convert the result to XML.
   • Extract concatenated strings from XML using the TYPE and value() methods.

4. Group by ID and use STUFF: to group results by ID. Use the STUFF function to remove leading delimiters (for example, commas) from connection strings.

5. Select Final result: Selects ID and concatenated Name and Value strings as Column columns.

6. Delete temporary table: Delete the temporary table after the operation is completed.

This approach leverages the power of FOR XML and PATH to efficiently concatenate strings in a GROUP BY operation without using cursors, loops, or user-defined functions.

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