Shivendra: It looks to me based on your example that you are creating a "smart field" where the first three chars are some sort of category and the numeric part is "random". If you example is accurate then a char(3) field and a standard auto_increment field will do the trick. If uniqueness is necessary use a composite index. If a "smart field" is truly required then the trigger with hash suggestion is a good one, however: Suggestions to use a hash are a problem because once you have a few million rows the likelihood of a collision is quite high if you cannot afford an error stopping your application. This means that if you write a trigger (the obvious way to go) you will need to trap any uniqueness violation and try again with different salt. Hope this helps a bit Boyd
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