How to create a unique sequence for each asset, other than the asset number?

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We need a unique sequence for each asset, other than the asset number or tag number. Currently the client has a number of 22 characters, being alphanumeric. We thought about maintaining this field via flexfield. Can we create a query that does this sequencing? Can we leave this flexfield open for filling in manual assets only? And, will everything that has AP as its source be automatically filled in via query?

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