Table relationships
Introduction First, let us look at the concept of the three basic relationships in a Relational Database defined based on the fundamental nature of Cardinality links between two tables: One-to-One Relationship (1-1) A record in Table A is linked to exactly one record in Table B and vice versa. Implemented by placing a Foreign Key in one of the two tables and assigning it a UNIQUE constraint. Examples: A User has only one UserProfile. A Product has only one ProductDetail. When to use: When splitting an oversized table containing rarely used columns to optimize data read performance. When security is required: Separating sensitive information such as credit cards or passwords into a dedicated table with stricter access controls. One-to-Many Relationship (1-N) A record in Table A can be linked to multiple records in Table B. Conversely, a record in Table B is linked to only one record in Table A. Implemented by placing a Foreign Key in the "Many" side table (Table B) pointing t...