How to Efficiently Create Comma-Delimited Lists in SQL Server?

Generating Comma-Separated Lists within SQL Server

This guide explains how to create comma-delimited lists from SQL Server tables. The methods leverage FOR XML PATH and STUFF for efficient list generation.

Understanding the Approach

The core technique combines FOR XML PATH('') to extract data as a string (without XML tags) and STUFF to replace spaces with commas. However, this approach has limitations.

Original Query Breakdown:

The original method uses FOR XML PATH('') to obtain data as a string. The data() alias, while seemingly an XML element, is a workaround that produces an error during XML generation, subsequently handled by the outer query. This error handling is less than ideal.

Improved Query:

A more robust solution is presented below:

<code class="language-sql">SELECT E1.deptno,
       STUFF((SELECT ', ' + E2.ename
               FROM emp AS E2
               WHERE E1.deptno = E2.DEPTNO
               FOR XML PATH('')), 1, 2, '')
FROM EMP AS E1
GROUP BY DEPTNO;</code>

This improved query directly concatenates values with commas, eliminating the error-prone XML workaround.

Advanced XML Handling:

To prevent potential issues with special XML characters, use .value for safer XML handling:

<code class="language-sql">SELECT E1.deptno,
       STUFF((SELECT ', ' + E2.ename
               FROM emp AS E2
               WHERE E1.deptno = E2.DEPTNO
               FOR XML PATH(''), TYPE)
               .value('.', 'NVARCHAR(MAX)'), 1, 2, '')
FROM EMP AS E1
GROUP BY DEPTNO;</code>

This final query offers the most reliable method for generating comma-separated lists in SQL Server, mitigating potential XML-related errors. The .value('.', 'NVARCHAR(MAX)') explicitly converts the XML output to a string, ensuring compatibility and preventing unexpected behavior.

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