Domain types for validation in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a domain named 'positive_int' that only allows integers greater than zero.

PostgreSQL

CREATE DOMAIN positive_int AS INTEGER CHECK (VALUE [1] 0);

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

A=

B>

C<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causes the domain to accept only negative numbers.

Using '=' restricts the domain to only zero, not positive numbers.

The domain 'positive_int' should only accept integers greater than zero, so the check condition uses > 0.

2fill in blank

medium

Complete the code to create a domain 'email_text' that only accepts text containing the '@' character.

PostgreSQL

CREATE DOMAIN email_text AS TEXT CHECK (POSITION('[1]' IN VALUE) > 0);

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

A%

B#

C$

D@

Attempts:

3 left

💡 Hint

Common Mistakes

Using '#' or '$' will not correctly validate email addresses.

Forgetting to check the position > 0 means the character might not be present.

The '@' character is essential in email addresses, so the check ensures it appears in the text.

3fill in blank

hard

Fix the error in the domain creation that should restrict a phone number to exactly 10 digits.

PostgreSQL

CREATE DOMAIN phone_number AS TEXT CHECK (LENGTH(VALUE) [1] 10);

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

A=

B>

C<>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' or '<' allows lengths other than 10.

Using '<>' means not equal, which is the opposite of the requirement.

The phone number must have exactly 10 digits, so the length must be equal to 10.

4fill in blank

hard

Fill both blanks to create a domain 'rating' that accepts integers between 1 and 5 inclusive.

PostgreSQL

CREATE DOMAIN rating AS INTEGER CHECK (VALUE [1] 1 AND VALUE [2] 5);

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

A>=

B<

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' or '<' excludes the boundary values 1 or 5.

Using '=' alone only allows one value, not a range.

The rating must be at least 1 (using >=) and at most 5 (using <=) to include both ends.

5fill in blank

hard

Fill all three blanks to create a domain 'zipcode' that accepts exactly 5 digits and only numeric characters.

PostgreSQL

CREATE DOMAIN zipcode AS TEXT CHECK (LENGTH(VALUE) [1] 5 AND VALUE ~ '[2]' AND VALUE !~ '[3]');

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

A=

B^[0-9]{5}$

C[^0-9]

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect regex patterns that allow letters or symbols.

Using '!=' instead of regex operators for pattern matching.

The zipcode must have length exactly 5 (using '='), match the regex for 5 digits (using '^[0-9]{5}$'), and not contain any non-digit characters (using '[^0-9]').

Practice

1. What is the main purpose of using domain types in PostgreSQL?

easy

A. To speed up query execution by indexing

B. To create custom data types with automatic validation rules

C. To store large binary data efficiently

D. To create temporary tables for session use

Solution

1. Step 1: Understand what domain types are

   Domain types are user-defined data types that include validation rules to ensure data quality.

2. Step 2: Identify the main purpose

   The main purpose is to enforce rules automatically when data is inserted or updated, keeping data clean.

3. Final Answer:

   To create custom data types with automatic validation rules -> Option B

4. Quick Check:

   Domain types = custom types with validation [OK]

Hint: Domains add rules to types, not speed or storage [OK]

Common Mistakes:

• Confusing domains with indexing
• Thinking domains store large files
• Mixing domains with temporary tables

2. Which of the following is the correct syntax to create a domain named positive_int that only allows positive integers?

easy

A. CREATE DOMAIN positive_int AS integer CHECK (VALUE > 0);

B. CREATE DOMAIN positive_int TYPE integer WHERE VALUE > 0;

C. CREATE DOMAIN positive_int AS integer VALIDATE (VALUE > 0);

D. CREATE DOMAIN positive_int AS integer IF VALUE > 0;

Solution

1. Step 1: Recall the correct syntax for domain creation

   The syntax is: CREATE DOMAIN name AS base_type CHECK (condition);

2. Step 2: Match the syntax with options

   CREATE DOMAIN positive_int AS integer CHECK (VALUE > 0); matches the correct syntax with CHECK and VALUE keyword.

3. Final Answer:

   CREATE DOMAIN positive_int AS integer CHECK (VALUE > 0); -> Option A

4. Quick Check:

   CREATE DOMAIN ... AS ... CHECK(...) [OK]

Hint: Use CHECK with VALUE keyword in domain creation [OK]

Common Mistakes:

• Using TYPE instead of AS
• Using WHERE or VALIDATE instead of CHECK
• Missing parentheses around condition

3. Given the domain creation:

CREATE DOMAIN us_zipcode AS varchar(5) CHECK (VALUE ~ '^[0-9]{5}$');

What will happen if you try to insert '1234a' into a table column of type us_zipcode?

medium

A. The insert will succeed because it's a varchar

B. The insert will cause a syntax error

C. The insert will succeed but store NULL instead

D. The insert will fail due to the CHECK constraint violation

Solution

1. Step 1: Understand the domain's CHECK constraint

   The domain requires the value to match exactly 5 digits using a regular expression.

2. Step 2: Check the value '1234a' against the regex

   '1234a' contains a letter, so it does not match the pattern of 5 digits.

3. Final Answer:

   The insert will fail due to the CHECK constraint violation -> Option D

4. Quick Check:

   Regex check fails = insert rejected [OK]

Hint: Regex in CHECK rejects invalid patterns [OK]

Common Mistakes:

• Assuming varchar allows any string without checks
• Thinking invalid data stores as NULL automatically
• Confusing constraint violation with syntax error

4. You have this domain:

CREATE DOMAIN non_empty_text AS text CHECK (LENGTH(VALUE) > 0);

Which of the following INSERT statements will cause an error when inserting into a column of type non_empty_text?

medium

A. INSERT INTO table_name (col) VALUES ('');

B. INSERT INTO table_name (col) VALUES ('world');

C. INSERT INTO table_name (col) VALUES (' ');

D. INSERT INTO table_name (col) VALUES (' hello ');

Solution

1. Step 1: Understand the CHECK condition

   The domain requires text length to be greater than 0, so empty strings fail. Whitespace-only strings pass as they have length > 0.

2. Step 2: Evaluate each insert value

   INSERT INTO table_name (col) VALUES (''); inserts an empty string '', length 0, violating the check.

3. Final Answer:

   INSERT with empty string '' causes error -> Option A

4. Quick Check:

   Empty string fails length > 0 check [OK]

Hint: Empty strings fail length > 0 check [OK]

Common Mistakes:

• Thinking whitespace strings fail (they pass)
• Assuming empty string is allowed
• Confusing syntax errors with constraint errors

5. You want to create a domain rating that stores integers from 1 to 5 inclusive. Which domain definition correctly enforces this range and can be used in multiple tables?

hard

A. CREATE DOMAIN rating AS integer WHERE (VALUE BETWEEN 1 AND 5);

B. CREATE DOMAIN rating AS integer CHECK (VALUE > 1 AND VALUE < 5);

C. CREATE DOMAIN rating AS integer CHECK (VALUE >= 1 AND VALUE <= 5);

D. CREATE DOMAIN rating AS integer CHECK (VALUE IN (1, 2, 3, 4));

Solution

1. Step 1: Understand the required range

   The rating must include 1 and 5, so boundaries are inclusive.

2. Step 2: Analyze each CHECK condition

   The option using WHERE instead of CHECK has invalid syntax.
   CREATE DOMAIN rating AS integer CHECK (VALUE > 1 AND VALUE < 5); excludes 1 and 5.
   CREATE DOMAIN rating AS integer CHECK (VALUE >= 1 AND VALUE <= 5); uses >= 1 AND <= 5, correctly including boundaries.
   CREATE DOMAIN rating AS integer CHECK (VALUE IN (1, 2, 3, 4)); uses IN list which misses 5.

3. Step 3: Choose the best option for clarity and standard usage

   CREATE DOMAIN rating AS integer CHECK (VALUE >= 1 AND VALUE <= 5); is clear, standard, and commonly used for range checks.

4. Final Answer:

   CREATE DOMAIN rating AS integer CHECK (VALUE >= 1 AND VALUE <= 5); -> Option C

5. Quick Check:

   Inclusive range uses >= and <= [OK]

Hint: Use >= and <= for inclusive numeric domain checks [OK]

Common Mistakes:

• Using > and < excludes boundary values
• Using WHERE instead of CHECK
• Incomplete IN list misses values