When working with data, you often need to manipulate strings to extract meaningful information. A common scenario is having strings with segments separated by underscores (_), and you only need the last segment. For example, you might have strings like:

• DATA_SET_001_SUMMARY
• DATA_SET_002_DETAILS
• DATA_SET_003_OVERVIEW
• DATA_SET_004_HEADER

In this blog post, we’ll explore how to extract the last segment of these strings using SQL Server’s string functions.

Scenario

Imagine you have a table named data_records with a column record_name that contains strings in the format mentioned above. Your task is to extract the last segment after the final underscore.

Solution

To achieve this in SQL Server, we can use a combination of the SUBSTRING, CHARINDEX, and REVERSE functions.

Step-by-Step Guide

1. Understanding the Functions:
   • REVERSE: This function reverses the string. For example, REVERSE('DATA_SET_001_SUMMARY') will return 'YRAMMUS_100_TES_ATAD'.
   • CHARINDEX: This function returns the position of a specified character or substring within a string. When used with REVERSE, it helps find the position of the last underscore.
   • SUBSTRING: This function extracts a portion of the string based on a starting position and length.

Constructing the Query:

Here’s the SQL query that extracts the last segment:

SELECT
    record_name,
    SUBSTRING(record_name, CHARINDEX('_', REVERSE(record_name)) + 1, LEN(record_name)) AS last_part
FROM
    data_records;

• REVERSE(record_name): Reverses the string.
• CHARINDEX('_', REVERSE(record_name)) + 1: Finds the position of the first underscore in the reversed string and adjusts it to match the original string’s position.
• SUBSTRING(record_name, ...): Extracts the substring from the position after the last underscore to the end of the string.

Example Result

If you run the query on a dataset with the following record_name values:

record_name
DATA_SET_001_SUMMARY
DATA_SET_002_DETAILS
DATA_SET_003_OVERVIEW
DATA_SET_004_HEADER

The result will be:

record_name	last_part
DATA_SET_001_SUMMARY	SUMMARY
DATA_SET_002_DETAILS	DETAILS
DATA_SET_003_OVERVIEW	OVERVIEW
DATA_SET_004_HEADER	HEADER

Conclusion

By using SQL Server’s string functions, you can easily extract specific segments of your data for further analysis or reporting. This approach is particularly useful in cases where you have standardized naming conventions and need to focus on specific parts of the string.