How to Generate Comma-Separated Lists from SQL Server Tables Using Queries?

SQL Server: Use query to generate comma separated list

Query explanation

This query is designed to create a comma separated list from a table, it utilizes the FOR XML PATH function to construct an XML fragment containing the required values. It uses a subquery to get the employee name (ename) for a specified department and then replaces the spaces in the XML fragment with commas.

SELECT 
    E1.deptno, 
    allemp = Replace ((SELECT E2.ename AS 'data()' 
                       FROM emp AS e2 
                       WHERE e1.deptno = e2.DEPTNO 
                       FOR xml PATH('')), ' ', ', ') 
 FROM EMP AS e1 
 GROUP BY DEPTNO; 

How FOR XML PATH works

FOR XML PATH('') generates an XML fragment for each row in the emp table based on the specified column (in this case, ename). Suppose there is a simple employee table:

<code>EmployeeID      Name
1               John Smith
2               Jane Doe</code>

The following query will create XML:

SELECT  EmployeeID, Name
FROM    emp.Employee
FOR XML PATH ('Employee');

Output:

<employee><employeeid>1</employeeid><name>John Smith</name></employee><employee><employeeid>2</employeeid><name>Jane Doe</name></employee>

Error handling and alternatives

The provided query attempts to use data() as an XML tag, which is invalid and will result in an error. To avoid this, you can use the following modified query:

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; 

This query ensures that no XML tags are created in the subquery, and it also handles names containing spaces by adding commas in the subquery.

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