Question at position 28 Management has requested that you build an employee database. You need to include each employee's current position and salary, as well as all prior positions and salaries with the company. You decide to use a one-to-many structure: an employee table with the main information such as name and address, and an employment table with position and salary history. You can use the employeeID field to connect them. What is employment.employeeID an example of? primary key foreign key alternate key secondary key单项选择题
A
primary key
B
foreign key
C
alternate key
D
secondary key

Question

Question at position 28 Management has requested that you build an employee database. You need to include each employee's current position and salary, as well as all prior positions and salaries with the company. You decide to use a one-to-many structure: an employee table with the main information such as name and address, and an employment table with position and salary history. You can use the employeeID field to connect them. What is employment.employeeID an example of? primary key foreign key alternate key secondary key单项选择题

A

primary key

B

foreign key

C

alternate key

D

secondary key

BlackTom AI · Accepted Answer

To tackle this question, I’ll examine what each term means in the context of relational databases and how it applies to the given one-to-many structure.
Option 1: primary key. A primary key uniquely identifies each row within the same table. The employment.employeeID field is not the unique identifier for the employment table itself; instead, it serves to link to the employee table. Therefore, it is not the primary key of the employment table.
Option 2: foreign key. A foreign key is a field (or collection of fields) in one table that references the primary key of another table, establishing a relationship between the two tables. In this scenario, employment.employeeID connects each employment record to the corresponding employee in the employee table, which fits the definition of a foreign key precisely.
Option 3: alternate key. An alternate key is a candidate key that could serve as a primary key but isn’t chosen as the primary key. Since employment.employeeID is specifically used to reference the employee table rather than serve as a unique identifier for the employment table itself, it does not function as an alternate key.
Option 4: secondary key. A secondary key is a non-primary key used for indexing and search purposes to improve queries, not primarily for establishing a referential link between tables. While an index on employeeID could exist, the core role of employment.employeeID in this design is to link records across tables, which is the job of a foreign key, not a secondary key.
In summary, the employment.employeeID field is best understood as a foreign key because it establishes the relationship from the employment table to the employee table by referencing the employee's primary key.

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