[Solved] You have a table Attendance with columns student_id, class_date, and session.... Which composite primary key should you define? | SQL

SQL - Table Constraints

You have a table Attendance with columns student_id, class_date, and session. You want to ensure each student can only have one attendance record per class date and session. Which composite primary key should you define?

A(class_date, session)

B(student_id, class_date)

C(student_id, class_date, session)

D(student_id, session)

Step-by-Step Solution

Solution:

Step 1: Understand uniqueness requirement
Each student must have only one record per class date and session, so all three columns combined must be unique.
Step 2: Choose composite key covering all uniqueness factors
Composite key must include student_id, class_date, and session to enforce this rule.
Final Answer:
(student_id, class_date, session) -> Option C
Quick Check:
Composite key covers all uniqueness columns [OK]

Quick Trick: Include all columns that define uniqueness in composite key [OK]

Common Mistakes:

MISTAKES

Leaving out session or class_date from key
Using only two columns when three needed
Confusing foreign keys with primary keys

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Which composite primary key should you define?

Step 1: Understand uniqueness requirement

Step 2: Choose composite key covering all uniqueness factors

Final Answer:

Quick Check:

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