in this case you would just overwrite the existing row, you wouldn’t use de-duplication because it would do the opposite of what you wanted in that case.

… That’s what I said, you’d just update the row, i.e. replace the existing data, i.e. overwrite what’s already there

Definitionally, the actual identity of the person MUST be unique, otherwise you’re going to somehow return two rows, when you call one, which is functionally impossible given how a DB is designed.

… I don’t think you understand how modern databases are designed

i genuinely cannot think of a single instance where you would want to delete one entry, and replace it with a reference to another

Well, there’s not always a benefit to keeping historical data. Sometimes you only want the most up-to-date information in a particular table or database, so you’d just update the row (replace). It depends on the use case of a given table.

what elon is implying here (remove “duplicate” entries, however that’s supposed to work)

Elon believes that each row in a table should be unique based on the SSN only, so a given SSN should appear only once with the person’s name and details on it. Yes, it’s an extremely dumb idea, but he’s a famously stupid person.

There can be duplicate SSNs due to name changes of an individual, that’s the easiest answer. In general, it’s common to just add a new record in cases where a person’s information changes so you can retain the old record(s) and thus have a history for a person (look up Slowly Changing Dimensions (SCD)). That’s how the SSA is able to figure out if a person changed their gender, they just look up that information using the same SSN and see if the gender in the new application is different from the old data.

Another accusation Elon made was that payments are going to people missing SSNs. The best explanation I have for that is that various state departments have their own on-premise databases and their own structure and design that do not necessarily mirror the federal master database. There are likely some databases where the SSN field is setup to accept strings only, since in real life, your SSN on your card actually has dashes, those dashes make the number into a string. If the SSN is stored as a string in a state database, then when it’s brought over to the federal database (assuming the federal db is using a number field instead of text), there can be some data loss, resulting in a NULL.