MySQL - Unique but not that Unique Please
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I have a varchar field (in table of a mysql database) where I need each entry to be unique compared to any other row of that same field of the entire set.

However, after I delete one of these unique strings, I want the ability to insert and update other records of this field, so that they now have this previously used unique value.

The problem is that the Unique constraint seems to remember all "deleted unique strings", and it won't allow me to update or add strings that were previously used (but are now deleted).

Is there another constraint, where I can specify that the set must be distinct at all times, but previously deleted unique varchars are not restrained?