Understanding GSM vs Non-GSM Characters

The GSM character set is a standardized collection of characters used in SMS messaging. Let’s explore how to identify and validate these characters in SQL Server.

GSM Character Set Overview

The GSM (GSM 3.38) character set includes:

Basic Latin alphabet (A-Z, a-z)
Numbers (0-9)
Special characters (@£$¥èéùìòÇØøÅåΔ_ΦΓΛΩΠΨΣΘΞÆæßÉ)
Punctuation marks (!”#¤%&’()*+,-./:;<=>?¡)
Extended characters (ÄÖÑÜ§¿abcdefghijklmnopqrstuvwxyzäöñüà)

Implementation Approaches

An Optimized SQL Server Implementation

CREATE FUNCTION dbo.IsGSM(@inputString NVARCHAR(MAX))
RETURNS BIT
AS
BEGIN
    DECLARE @gsmCharacterSet NVARCHAR(MAX) =
    ' @£$¥èéùìòÇØøÅåΔ_ΦΓΛΩΠΨΣΘΞÆæßÉ!""#¤%&''()*+,-./0123456789:;<=>?¡ABCDEFGHIJKLMNOPQRSTUVWXYZÄÖÑÜ§¿abcdefghijklmnopqrstuvwxyzäöñüà'

    DECLARE @isNonGSM BIT = 0
    DECLARE @i INT = 1
    DECLARE @char NVARCHAR(1)

    WHILE @i <= LEN(@inputString)
    BEGIN
        SET @char = SUBSTRING(@inputString, @i, 1)
        IF CHARINDEX(@char, @gsmCharacterSet) = 0
        BEGIN
            SET @isNonGSM = 1
            BREAK
        END
        SET @i = @i + 1
    END

    RETURN 1^@isNonGSM
END

Efficient character-by-character validation
Clear implementation logic
Easy to maintain and modify
Handles NULL inputs gracefully
May be slower for very long strings
Requires careful character set maintenance

Regular Expression Approach

SQL Server isn’t known to fully support Regular Expressions or this would have been the preferred implementation. Since it’s much in demand, support for regular expressions should get stronger. Please do check if the latest version of SQL Server has this feature.

References

https://en.wikipedia.org/wiki/GSM_03.38