NOT NULL constraint behavior in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a table where the 'name' column cannot be empty.

SQL

CREATE TABLE users (id INT, name VARCHAR(100) [1]);

Drag options to blanks, or click blank then click option'

ANULL

BNOT NULL

CDEFAULT NULL

DPRIMARY KEY

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL instead of NOT NULL allows empty values.

Using PRIMARY KEY when you only want to prevent nulls.

The NOT NULL constraint ensures that the 'name' column must have a value and cannot be left empty.

2fill in blank

medium

Complete the INSERT statement to add a user with a non-empty 'email' field that has a NOT NULL constraint.

SQL

INSERT INTO users (id, email) VALUES (1, [1]);

Drag options to blanks, or click blank then click option'

A'[e-mail]'

BDEFAULT

C''

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Inserting NULL into a NOT NULL column causes an error.

Using empty string '' may be allowed but is often not meaningful.

You must provide a valid non-null value for the 'email' column because it has a NOT NULL constraint. Using '[e-mail]' is correct.

3fill in blank

hard

Fix the error in the table creation by adding the correct constraint to the 'age' column to prevent NULL values.

SQL

CREATE TABLE people (id INT, age INT [1]);

Drag options to blanks, or click blank then click option'

AUNIQUE

BDEFAULT 0

CCHECK (age > 0)

DNOT NULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using DEFAULT 0 does not prevent NULL values.

CHECK constraints do not prevent NULL unless specified.

The NOT NULL constraint ensures the 'age' column cannot have NULL values, fixing the error.

4fill in blank

hard

Fill both blanks to create a table where 'username' cannot be NULL and has a default value 'guest'.

SQL

CREATE TABLE accounts (id INT, username VARCHAR(50) [1] [2]);

Drag options to blanks, or click blank then click option'

ANOT NULL

BDEFAULT 'guest'

CUNIQUE

DPRIMARY KEY

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNIQUE instead of NOT NULL does not prevent NULL values.

Forgetting to set DEFAULT causes errors when no value is given.

The NOT NULL constraint prevents NULL values, and DEFAULT 'guest' sets a default username if none is provided.

5fill in blank

hard

Fill all three blanks to insert a new row with id 10, a non-null name, and a default age in the 'persons' table.

SQL

INSERT INTO persons (id, name, age) VALUES ([1], [2], [3]);

Drag options to blanks, or click blank then click option'

A10

B'Alice'

CDEFAULT

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL for age when it has a NOT NULL constraint causes error.

Not quoting the name string causes syntax error.

We insert 10 for id, a non-null name 'Alice', and use DEFAULT for age to apply the default value.