Effective Techniques to Combine Data into One Column using T-SQL (SQL Server 2005 and Earlier)

This method leverages string manipulation functions to concatenate values into a single string.

Example:

SELECT CustomerID,
       (
           SELECT STUFF((
               SELECT ',' + CAST(OrderID AS VARCHAR(10))
               FROM Orders
               WHERE Orders.CustomerID = Customers.CustomerID
               FOR XML PATH('')
           ), 1, 1, '')
       ) AS OrderList
FROM Customers;

Explanation:

1. The inner SELECT uses FOR XML PATH('') to convert OrderID values from the Orders table into an XML fragment for each customer.
2. STUFF removes the leading comma (",") and combines the remaining comma-separated OrderID values into a single string stored in the OrderList column.

Using CONCAT:

For simpler scenarios with only a few columns, you can use the + operator for string concatenation.

SELECT CustomerID,
       FirstName + ' ' + LastName AS FullName
FROM Customers;

User-Defined Functions (UDFs):

For complex scenarios or reusability, you can create a UDF that accepts multiple values and combines them into a desired format.

Example (simplified):

CREATE FUNCTION CombineValues (@value1 NVARCHAR(50), @value2 NVARCHAR(50))
RETURNS NVARCHAR(100)
AS
BEGIN
  DECLARE @result NVARCHAR(100);
  SET @result = @value1 + ' | ' + @value2;
  RETURN @result;
END;

SELECT CustomerID,
       CombineValues(FirstName, LastName) AS FullName
FROM Customers;

Related Issues and Solutions:

• Performance: Concatenating strings can be less performant than using separate columns. If performance is critical, consider alternative approaches like storing data in separate columns and processing them later.
• Data Integrity: Combining values into a single column can make data manipulation and analysis more complex. Evaluate if this approach truly simplifies your task and doesn't introduce additional challenges.