Question

A table has two candidate keys, one of which is chosen as the primary key. How many alternate keys does this table have?

• A. 0
• B. 1
• C. 2
• D. 3

Hint:

Alternate keys = candidate keys - primary key. Here that is 2 - 1.

Answer 1

The Correct Option is B

Step 1: Recall the key terms:
A candidate key is a column (or set of columns) that can identify every row uniquely.
A table can have many candidate keys.
The designer picks one of them as the primary key.
Every candidate key that is not picked is called an alternate key.

Step 2: Use the formula:
Number of alternate keys = number of candidate keys - number of primary keys.
A table always has exactly one primary key.

Step 3: Put in the numbers:
Candidate keys = 2.
Primary key = 1.
Alternate keys = 2 - 1 = 1.

Step 4: Check each option:
Option (A) 0 would mean both candidate keys became the primary key, which is not allowed.
Option (B) 1 matches our result, so it is correct.
Option (C) 2 counts all the candidate keys and forgets to remove the primary key.
Option (D) 3 is more than the number of candidate keys, so it is impossible.

Final Answer:
The table has 1 alternate key. This is option (B).