Wonder what the [check-constraints] part meant or if it's a placeholder.

“I intentionally wrote the example code the way a beginner might. More experienced users would probably reach for solutions like: Updating and checking the balance in a single UPDATE Using [check constraints]to ensure an account balance can never be negative.” Not the author but presumably ALTER TABLE foo ‘ADD CONSTRAINT BalanceCantBeNegative CHECK( balance >= 0 )’

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