In a table Employee with columns EmployeeID, Email, and PhoneNumber, which of the following could be considered a candidate key?
Question
In a table Employee with columns EmployeeID, Email, and PhoneNumber, which of the following could be considered a candidate key?
Solution 1
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:
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EmployeeID: This could be a candidate key if each EmployeeID is unique to each employee.
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Email: This could be a candidate key if each employee has a unique email address.
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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.
Solution 2
A candidate key in a database is a unique identifier - it cannot have any duplicate values. In the context of the Employee table, any of the following could be considered a candidate key:
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EmployeeID: This is often used as a primary key in databases, and is typically a unique identifier for each employee. If each EmployeeID is unique, then it could be a candidate key.
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Email: This could also be a candidate key, assuming that each employee has a unique email address. In many systems, this is a safe assumption, as employees often have email addresses based on their names and/or employee ID.
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PhoneNumber: This could potentially be a candidate key, but it's less likely than the other two options. Phone numbers can change more frequently than the other two, and it's also possible for multiple employees to share a phone number (for example, if they share a desk or work in the same office).
So, EmployeeID and Email are the most likely candidate keys, but PhoneNumber could also be a candidate key under the right circumstances.
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