T-SQL Techniques for Splitting Strings

Introduction

In T-SQL, splitting strings is a common task, especially when dealing with CSV data or similar formats. Different methods can be employed depending on your SQL Server version and specific requirements. This tutorial explores several effective techniques to split strings in T-SQL, focusing on SQL Server 2008 R2.

Using User-Defined Functions

For versions like SQL Server 2008 R2 that lack built-in string splitting functions, user-defined functions (UDFs) can be a powerful solution. Below is an example of creating a function to split strings by a specified delimiter:

CREATE FUNCTION dbo.SplitString (
    @stringToSplit VARCHAR(MAX),
    @delimiter CHAR(1)
)
RETURNS TABLE
AS
RETURN (
    WITH StringParts AS (
        SELECT 
            CAST(NULL AS NVARCHAR(255)) AS Value,
            @stringToSplit + @delimiter AS Remainder
        UNION ALL
        SELECT 
            LTRIM(RTRIM(SUBSTRING(
                Remainder, 1, CHARINDEX(@delimiter, Remainder) - 1))),
            SUBSTRING(
                Remainder, CHARINDEX(@delimiter, Remainder) + 1,
                LEN(Remainder))
        FROM StringParts
        WHERE CHARINDEX(@delimiter, Remainder) > 0
    )
    SELECT Value 
    FROM StringParts
    WHERE Value IS NOT NULL
);

How to Use the Function

To use this function, simply call it in a query with your string and delimiter:

SELECT * FROM dbo.SplitString('91,12,65,78,56,789', ',')

Using XML Conversion

Another approach involves converting strings into XML format. This method is versatile and allows you to split strings without requiring additional tables or recursive logic.

Converting Strings Without Additional Tables

Here’s how you can transform a delimited string into rows using XML:

DECLARE @String VARCHAR(100) = 'String1,String2,String3';
DECLARE @Delimiter CHAR = ',';

SELECT LTRIM(RTRIM(value)) AS Value 
FROM (
    SELECT CAST('<M>' + REPLACE(@String, @Delimiter, '</M><M>') + '</M>' AS XML)
) AS A
CROSS APPLY A.nodes('/M') AS Split(Value);

Converting Strings From a Table

If your data is already stored in a table and each row needs to be split:

DECLARE @Delimiter CHAR = ',';

SELECT ID, LTRIM(RTRIM(value)) AS Value 
FROM (
    SELECT 
        ID,
        CAST('<M>' + REPLACE(Value, @Delimiter, '</M><M>') + '</M>' AS XML) AS Data
    FROM YourTableName
) AS A
CROSS APPLY A.nodes('/M') AS Split(Value);

Best Practices and Tips

Performance Considerations: When dealing with large datasets or frequent operations, consider the performance implications of each method. User-defined functions are straightforward but might not scale well for extremely large strings.
Delimiter Handling: Ensure your delimiter is unique within the string to avoid incorrect splits.
Error Handling: Always include error handling in production environments to manage unexpected data formats gracefully.

Conclusion

Splitting strings in T-SQL can be achieved through various methods, each with its strengths and limitations. Whether you use a user-defined function or XML conversion, understanding these techniques allows for flexible and efficient data manipulation in SQL Server 2008 R2 and beyond.