![]() ![]() To do this we’ll fall back on one of our favorite T-SQL constructs: the Tally table. The best-practice approach is to split that string so each character appears as a separate row. In T-SQL, it is relatively awkward to do this directly to each character in a string, particularly when the string is not of fixed length. Most check digit calculation algorithms require applying some transformation to each digit in a string. Such proofs are beyond the scope of this article. From this, you can arrive at a probability distribution that describes how efficient the algorithm is in avoiding these transcription errors. Numerical methods exist that can generate all of the possible transcription errors of the types described for a given length string, and these can then be assembled into test strings to be applied against the check digit algorithm. Phonetic errors, which can occur when someone tells you a number over the phone, like hearing 17 when the caller said 70.Jump twin errors, such as 282 instead of 181, which can easily occur if both hands are engaged in typing in the number using the number keys above the letters on the keyboard, when one of the hands is offset by one key position.Jump transposition errors, which involve incorrect arrangement of a multi-digit sequence, such as 729 instead of 972. ![]()
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