What is a candidate key?

• The first column of every table
• A smallest set of columns that names each row alone
• Any column that holds numbers

The table rule is student ID -> email. What does it promise?

• Each ID always pairs with the same email
• Each email always pairs with the same ID
• Every student shares a single email

A table is in Boyce-Codd form exactly when every dependency starts from a candidate key.

Circle one:   True   False

A table holds ID, email, and dorm, with ID -> email and email -> dorm. Which set is a candidate key?

• {ID}
• {email}
• {ID, email}

Columns are A, B, C, with rules A -> B and B -> C. What is the closure of {A}?

• {A, B}
• {A}
• {A, B, C}

Rules are A -> B, B -> C, C -> D. Starting from {A}, how many of the 4 columns does the closure reach?

Answer: ______________

The rule email -> dorm violates BCNF in a table of ID, email, and dorm. How do you repair the table?

• Delete the dorm column entirely
• Add rows until email can name every row
• Split into ID with email plus email with dorm, then join back to check

Pat claims a table with email -> dorm is in BCNF because email holds no duplicates today. What is wrong?

• A key must be a single column, never a set
• A rule is judged by what must hold, and email still cannot name a row
• BCNF only cares about numeric columns, not emails