Assuming SQL Server:
e.g. if you class special characters as anything NOT alphanumeric:
DECLARE @MyString VARCHAR(100)
SET @MyString = 'adgkjb$'
IF (@MyString LIKE '%[^a-zA-Z0-9]%')
PRINT 'Contains "special" characters'
ELSE
PRINT 'Does not contain "special" characters'
Just add to other characters you don't class as special, inside the square brackets
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