Today, I encountered a situation where I needed to display all related data in a comma-separated list using a SELECT statement. Up until now, I have been using a scalar function that utilizes COALESCE() to achieve this. However, I discovered a fantastic solution that allows us to generate a comma-separated list without needing a scalar function. Let’s dive into it with SQLYoga guide.

Example Scenario

Consider the following table:

CREATE TABLE #test(    
field1 VARCHAR(5),     
field2 VARCHAR(5)
);

Let’s insert some data into this table:

INSERT INTO #test
SELECT '001','AAA'
UNION ALL
SELECT '001','BBB'
UNION ALL
SELECT '002','CCC'
UNION ALL
SELECT '003','DDD'
UNION ALL
SELECT '004','EEE'
UNION ALL
SELECT '004','FFF'
UNION ALL
SELECT '004','GGG';

Current Data in the Table

After inserting the data, our table looks like this:

Expected Output

We want to generate a comma-separated list of field2 for each unique field1. The expected output is:

Proposed Solution

Here’s the SQL query to achieve the desired output:

SELECT field1,    
SUBSTRING(        
(            
SELECT ', ' + field2            
FROM #test t2            
WHERE t1.field1 = t2.field1            
ORDER BY t2.field2            
FOR XML PATH('')        
), 3, 1000) AS field2_list
FROM #test t1
GROUP BY field1;

Explanation

Subquery with FOR XML PATH: The subquery concatenates field2 values into a single string separated by commas for each field1. The FOR XML PATH('') clause converts the result into XML format, which we then transform into a plain string.
Substring Function: The SUBSTRING function removes the leading comma and space from the concatenated string. The 3 indicates starting from the third character, effectively skipping the first two characters (, ).
Group By: The GROUP BY clause ensures we get one row per field1.

Output

Running the above query will yield the following output:

With this approach, you can generate a comma-separated list without relying on scalar functions. This method is efficient and leverages SQL Server’s XML capabilities to concatenate strings.

Read More on SQLYoga about advanced SQL techniques and optimizing your queries.

At SQLYoga, we are committed to bringing you the latest and most efficient SQL Server solutions. This method of generating a comma-separated list is a prime example of how you can streamline your SQL queries and achieve better performance. Stay tuned for more tips and tricks to enhance your SQL skills and streamline your database management tasks.

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