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Is a Composite UNIQUE Constraint On an Already UNIQUE Column Redundant?

1 vote
2 answers
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I'd just like to clarify something pretty simple regarding single and composite UNIQUE constraints that I can't find a clear answer to. Assume I have the following table:
CREATE TABLE person (
  id INT PRIMARY KEY,
  customer_id INT NOT NULL UNIQUE,
  name VARCHAR(20) NOT NULL
  ...
)
Would it be safe to say that adding the following constraint:
UNIQUE(customer_id, name)
would be redundant and offer no benefit under any circumstance? In other words, is it useless to create a composite UNIQUE constraint that includes a column which is already UNIQUE? This appears to make logical sense, but as I stated, I couldn't find an answer confirming it.
Asked by Twisted Tea (111 rep)
Sep 5, 2023, 09:25 PM
Last activity: May 21, 2025, 10:05 PM