hardMultiple Select
FC0-U71 Practice Question: Which THREE of the following are valid database…
Which THREE of the following are valid database integrity constraints?
⚠ Common exam trap
Many candidates confuse database objects like indexes with integrity constraints, or they invent terms like 'CONDITION' because it sounds similar to the valid CHECK constraint, leading them to select incorrect options.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
UNIQUE
UNIQUE (A) is a valid integrity constraint because it enforces that all values in a column or set of columns are distinct, preventing duplicate entries and supporting entity integrity. FOREIGN KEY (C) is valid because it enforces referential integrity by requiring that values in a child table match existing values in a parent table's primary or unique key. PRIMARY KEY (E) is valid because it uniquely identifies each row and implicitly enforces both uniqueness and NOT NULL, forming the core entity integrity constraint. INDEX (B) is not a constraint but a performance structure that speeds up data retrieval, and CONDITION (D) is not a standard SQL integrity constraint, as validity checks are implemented through CHECK constraints rather than a generic CONDITION keyword.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
UNIQUE
Why this is correct
UNIQUE enforces entity integrity by preventing duplicate values in a column, ensuring each row can be uniquely identified. It is a standard SQL constraint applied at table definition, satisfying the question's requirement for a valid database integrity constraint.
- ✗
INDEX
Why it's wrong here
INDEX is a physical access structure that speeds row retrieval; it enforces no rule on the data itself, so it cannot constrain values. It is legitimately created on columns to improve query performance, which is why it is confused with constraints such as PRIMARY KEY or UNIQUE.
- ✓
FOREIGN KEY
Why this is correct
FOREIGN KEY enforces referential integrity by requiring values in one table to match existing values in a referenced table's primary key. This prevents orphaned records and is a standard SQL constraint, making it a valid database integrity constraint.
- ✗
CONDITION
Why it's wrong here
CONDITION is not a database constraint keyword; valid constraints are PRIMARY KEY, FOREIGN KEY, UNIQUE, CHECK, NOT NULL and DEFAULT. It is tempting because CHECK enforces a logical condition on column values, so 'condition' sounds like a synonym, but the SQL syntax requires CHECK, not CONDITION.
- ✓
PRIMARY KEY
Why this is correct
PRIMARY KEY enforces entity integrity by uniquely identifying each row and implicitly disallowing NULL values. It is a standard SQL constraint applied at table creation, satisfying the question's requirement for a valid database integrity constraint.
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