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It is not a question of copying the indexes, but of mfd_id being special. If you insert a list of mfd_id values into a table, whether new or existing, with that field name, then Manifold will automatically attempt to build or manage a BTREE index on the field. As soon as a duplicate value arises, the insert must fail (since mfd_id must always be unique). So in general, avoid inserting mfd_id vales into a new or existing table. You can do it, if you are certain that the values are (and will remain) unique. Then it is handled perfectly. But usually there is no need to. Instead, usually, if you need source mfd_id values in the target, rename them into a field with a different name (without a BTREE index). Such as source_id.
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