Convert Comma-Separated Values from a Single Row into Multiple Rows in MSSQL

Introduction:-

Handling comma-separated values (CSV) is a common requirement in database management, especially when working with data that needs to be parsed into multiple rows for easier processing, analysis, or integration. For example, you may encounter scenarios where a single column in a database contains delimited values , and you need to break these values into individual rows for further processing.

This approach is particularly useful when:

The database structure or application cannot store multiple values in separate rows by default.

You need to process or query individual elements of a delimited list.

Integration tasks or reporting requires a normalized format.

In SQL Server, we can efficiently convert such comma-separated values into multiple rows using a Common Table Expression (CTE).

Why Do We Need This:-

Normalization: De normalized data (comma-separated values in a single column) can be harder to manage and query. Splitting them into rows aligns with database normalization principles.

Simpler Queries: Queries and operations (e.g., aggregations, filtering) become more straightforward when working with separate rows rather than parsing string data repeatedly.

Scalability: Converting CSV data into rows allows you to integrate and analyze data more effectively, especially in large-scale datasets.

How to Solve:-

Using mysql server for execution:

Code Execution:

Below is the solution to convert a comma-separated string into multiple rows using a recursive Common Table Expression (CTE):

DECLARE @T VARCHAR(100) = ‘Where,there,is,a,will,there,is,a,way’;

— Append a comma at the end to simplify parsing

SET @T = @T + ‘,’;

;WITH MyCTE(Start, [End]) AS (

— Anchor Member: Find the position of the first comma

SELECT

1 AS Start,

CHARINDEX(‘,’, @T, 1) AS [End]

UNION ALL

— Recursive Member: Continue finding commas after the previous one

SELECT

[End] + 1 AS Start,

CHARINDEX(‘,’, @T, [End] + 1) AS [End]

FROM MyCTE

WHERE [End] < LEN(@T) — Stop when the last comma is reached

)

— Extract substrings based on the calculated Start and End positions

SELECT

SUBSTRING(@T, Start, [End] – Start) AS Value

FROM MyCTE

WHERE [End] > 0; — Ensure valid positions

Explanation of the Query:

1.Initialization:

a.The string @T is defined with the input CSV data. A comma is appended to the end to ensure all values, including the last one, are processed.

2.CTE Logic:

a.Anchor Member: Finds the position of the first comma using CHARINDEX.

b.Recursive Member: Finds subsequent commas by starting from the position of the last detected comma and continuing until the end of the string.

3.Substring Extraction:

a.The SUBSTRING function extracts parts of the string between the starting position (Start) and the next comma (End).

4.Output:

a.Each extracted substring is returned as a row in the result set.

Conclusion:-

Converting comma-separated values into multiple rows in SQL Server is a practical and efficient technique for normalizing data and making it easier to query, analyze, and integrate with other systems. Using a recursive Common Table Expression (CTE) provides a dynamic and scalable solution that can handle varying lengths of input with minimal complexity.

Narmadha Dhatchinamurdhy