In an ERD, what does a cardinality of "One-to-One" signify?

Each entity in the first table can be related to at most one entity in the second table
Each entity in the first table can be related to multiple entities in the second table
Each entity in the first table can be related to only one entity in the second table
Each entity in the first table can be related to only one entity in the second table, and vice versa

A cardinality of "One-to-One" in an ERD signifies that each entity in the first table can be related to only one entity in the second table, and vice versa. This type of relationship is less common but is useful in certain scenarios where a strict one-to-one association is needed.

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