Composite keys need a complete pair match when the allowed values are defined together. I don’t split the components into independent lists. Doing so can admit combinations that were never allowed.
IIF and CASE: Control Return Types and Use Typed NULL Values
IIF and CASE choose result values, but their branches also define a shared return type. I make that type explicit when mixed inputs could surprise the reader. Typed NULL values help describe the same output contract.
SQL SERVER – Primary Key Constraints and Unique Key Constraints
Primary Key and Unique Key both enforce uniqueness, but they differ in the index they create and in NULL handling. Here are the differences and the scripts.