How to Retrieve Multiple Values from a Single Column in SQL Server Using T-SQL?

T-SQL Techniques for Retrieving Multiple Values from a Single Column

In SQL Server database management, efficiently retrieving multiple values associated with a single record is a common task. This often involves tables with a one-to-many relationship, where a single identifier links to multiple related values. This article demonstrates a robust method using T-SQL functions and string manipulation.

Consider a UserAliases table where each user can have several aliases. The challenge lies in retrieving all aliases for a specific user into a single column. This can be elegantly solved by combining the COALESCE function with a user-defined function.

The following T-SQL code illustrates this solution:

CREATE FUNCTION [dbo].[GetAliasesById] (@userID INT)
RETURNS VARCHAR(MAX)
AS
BEGIN
    DECLARE @output VARCHAR(MAX);
    SELECT @output = COALESCE(@output + ', ', '') + alias
    FROM UserAliases
    WHERE userid = @userID;
    RETURN @output;
END;
GO

SELECT UserID, dbo.GetAliasesByID(UserID) AS Aliases
FROM UserAliases
GROUP BY UserID;
GO

The GetAliasesById function takes a userID as input and returns a comma-separated string of all associated aliases. COALESCE handles potential null values, ensuring a properly formatted output. The main SELECT statement then calls this function for each user, resulting in a single column containing all aliases for each user ID.

This approach provides a concise and efficient way to manage and display multiple values linked to a single entity, simplifying data handling within your T-SQL applications.

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