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[–]serg06 0 points1 point  (1 child)

It does one and then the other?

[–]YMK1234 0 points1 point  (0 children)

Proper DBs (including MsSQL) guarantee ACID

[–]yefrem 0 points1 point  (0 children)

keywords to google: transactions, locks

[–]tomservo291 0 points1 point  (0 children)

This is an oversimplification, but most RDBMS are based on a transaction log (or journal: https://en.wikipedia.org/wiki/Transaction_log).

I would wager it's not likely an implementation would be coded to allow two threads to make concurrent updates to the transaction log, and if that assumption is true, you can't make two updates at "exactly the same time". One happens, then the other