Integrity constraints in DBMS Theory - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a primary key constraint to the 'id' column.

DBMS Theory

ALTER TABLE employees ADD CONSTRAINT pk_employee_id [1] (id);

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APRIMARY KEY

BCHECK

CUNIQUE

DFOREIGN KEY

Attempts:

3 left

💡 Hint

Common Mistakes

Using FOREIGN KEY instead of PRIMARY KEY

Using UNIQUE which allows nulls

Using CHECK which is for conditions

The PRIMARY KEY constraint uniquely identifies each record in a table.

2fill in blank

medium

Complete the code to ensure the 'age' column cannot have NULL values.

DBMS Theory

ALTER TABLE persons MODIFY age [1];

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ANULL

BNOT NULL

CDEFAULT 0

DUNIQUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL which allows nulls

Using UNIQUE which only enforces uniqueness

Using DEFAULT which sets a default value but allows NULL

The NOT NULL constraint ensures a column cannot have NULL values.

3fill in blank

hard

Fix the error in the code to add a foreign key constraint referencing 'departments(id)'.

DBMS Theory

ALTER TABLE employees ADD CONSTRAINT fk_dept_id [1] (department_id) REFERENCES departments(id);

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AFOREIGN KEY

BPRIMARY KEY

CUNIQUE

DCHECK

Attempts:

3 left

💡 Hint

Common Mistakes

Using PRIMARY KEY instead of FOREIGN KEY

Using UNIQUE which does not create relationships

Using CHECK which is for conditions

The FOREIGN KEY constraint links a column to a primary key in another table.

4fill in blank

hard

Fill both blanks to create a check constraint that ensures salary is greater than 0.

DBMS Theory

ALTER TABLE employees ADD CONSTRAINT chk_salary [1] (salary [2] 0);

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ACHECK

B>

C<

DNOT NULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using NOT NULL which only prevents nulls

Using < instead of > causing wrong condition

Omitting CHECK keyword

The CHECK constraint enforces a condition on column values. Here, salary must be greater than 0.

5fill in blank

hard

Fill all three blanks to create a unique constraint on the combination of 'email' and 'phone' columns.

DBMS Theory

ALTER TABLE contacts ADD CONSTRAINT [1] UNIQUE ([2], [3]);

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Auq_email_phone

Bemail

Cphone

Dpk_contacts

Attempts:

3 left

💡 Hint

Common Mistakes

Using primary key name instead of unique constraint name

Swapping column names or missing one

Omitting the UNIQUE keyword

A UNIQUE constraint ensures that the combination of 'email' and 'phone' is unique across all rows. Naming the constraint helps identify it.