While denormalizing Employee and Contract tables to include ContractType, which join type preserves all rows from Employee and includes matching ContractType data?

While denormalizing Employee and Contract tables to include ContractType, which join type preserves all rows from Employee and includes matching ContractType data?

• A. Right outer
• B. Inner
• C. Left outer
• D. Full outer

Answer: (C)

Preserving all rows from the left table while bringing in matching data from the right is done with a left outer join. In this scenario, the Employee table is the left side, and you want every employee to appear in the result. A left outer join returns every row from Employee and adds the ContractType data when there’s a corresponding contract record. If an employee has no matching contract, the ContractType fields will be null, but the employee row is still included. This is why it’s the best choice here: inner joins would drop employees without a contract, right outer would preserve all contracts (not what you want), and full outer would bring in unmatched rows from both sides—more than needed for this denormalization. Denormalizing by pulling ContractType into Employee using a left join keeps the complete employee list intact while enriching records where contract data exists.

Preserving all rows from the left table while bringing in matching data from the right is done with a left outer join. In this scenario, the Employee table is the left side, and you want every employee to appear in the result. A left outer join returns every row from Employee and adds the ContractType data when there’s a corresponding contract record. If an employee has no matching contract, the ContractType fields will be null, but the employee row is still included.

This is why it’s the best choice here: inner joins would drop employees without a contract, right outer would preserve all contracts (not what you want), and full outer would bring in unmatched rows from both sides—more than needed for this denormalization. Denormalizing by pulling ContractType into Employee using a left join keeps the complete employee list intact while enriching records where contract data exists.