Consider the Baseball database used in a number of class examples. We enforced referential integrity for Teams and Batters. This means _________

Question

BlackTom AI · Accepted Answer

A foreign key in the Batters table must reference an existing row in the Teams table, so any batter record must point to a team that already exists.

1) Relevant knowledge points and concepts
- Primary key: a unique identifier in the parent table (Teams), e.g., team_id.
- Foreign key: an attribute in the child table (Batters) that references the parent's primary key (Batters.team_id → Teams.team_id).
- Referential integrity: a database constraint that ensures foreign key values are valid references to existing primary key values (prevents “dangling” references).

2) Step-by-step reasoning
- Identify the parent/child relationship: Teams is the parent, Batters is the child, since bombers/players belong to teams.
- Enforcing referential integrity means the DBMS checks every Batters.team_id on INSERT or UPDATE.
- If a Batters row tries to use a team_id that does not exist in Teams, the DBMS rejects the operation and raises a foreign key violation.

3) Intermediate (conceptual) steps / example
- Teams table contains {team_id: 1, name: "A"} and {team_id: 2, name: "B"}.
- Attempt to insert into Batters: {batter_id: 10, name: "Joe", team_id: 3}. Because 3 is not a team_id in Teams, the insert fails.

4) Why the correct answer is correct
- The statement "you cannot add a batter for which no team exists" exactly describes the foreign-key enforcement: child rows cannot reference non-existent parent rows.

5) Why the other options are incorrect
- "none of the other choices..." is false because one option does correctly describe referential integrity.
- "you cannot delete batters" is incorrect: referential integrity does not by itself prevent deleting child rows; it governs relationships from child to parent. Deleting batters is typically allowed.
- "you cannot add a team for which no batter exists" is reversed: referential integrity does not require that a parent must have children; teams can exist without batters.

6) Conclusion
This confirms the correct answer: you cannot add a batter for which no team exists.

Consider the Baseball database used in a number of class examples. We enforced referential integrity for Teams and Batters. This means _________ 单项选择题

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