In a table Employee with columns EmployeeID, Email, and PhoneNumber, which of the following could be considered a candidate key?

A candidate key in a database is a column, or set of columns, that can uniquely identify a record without any extraneous data. Each table can have more than one candidate key.

In the Employee table with columns EmployeeID, Email, and PhoneNumber, any of these could potentially be a candidate key, depending on the data:

1. EmployeeID: This could be a candidate key if each EmployeeID is unique to each employee.

2. Email: This could be a candidate key if each employee has a unique email address.

3. PhoneNumber: This could be a candidate key if each employee has a unique phone number.

However, the most common and reliable candidate key in this scenario would likely be EmployeeID, as it is common practice to assign each employee a unique ID. Email could also be a reliable candidate key, assuming all employees have unique email addresses. Phone numbers could potentially be shared (for example, two employees might share a home phone number), so it might be less reliable as a candidate key.

Remember, the key point of a candidate key is its ability to uniquely identify each record in the table.