Domain types for validation in PostgreSQL - Time & Space Complexity

Time Complexity: Domain types for validation

O(n)

Understanding Time Complexity

We want to understand how the time it takes to check data using domain types grows as we add more data.

How does validation time change when the number of rows increases?

Scenario Under Consideration

Analyze the time complexity of the following domain type validation.

CREATE DOMAIN positive_int AS INTEGER
  CHECK (VALUE > 0);

CREATE TABLE orders (
  order_id SERIAL PRIMARY KEY,
  quantity positive_int
);

INSERT INTO orders (quantity) VALUES (5), (10), (0); -- last will fail

This code creates a domain type that only allows positive integers and uses it to validate data on insert.

Identify Repeating Operations

Look at what happens when many rows are inserted or checked.

• Primary operation: Checking the domain constraint for each row inserted or updated.
• How many times: Once per row, for every row being inserted or updated.

How Execution Grows With Input

Each new row adds one more check to do.

Input Size (n)	Approx. Operations
10	10 checks
100	100 checks
1000	1000 checks

Pattern observation: The number of checks grows directly with the number of rows.

Final Time Complexity

Time Complexity: O(n)

This means the time to validate grows in a straight line as you add more rows.

Common Mistake

[X] Wrong: "The domain validation happens once for the whole table, so time stays the same no matter how many rows."

[OK] Correct: Each row is checked separately when inserted or updated, so more rows mean more checks and more time.

Interview Connect

Understanding how validation scales helps you design databases that stay fast as data grows. This skill shows you think about real-world data handling.

Self-Check

"What if the domain check was more complex, like checking a pattern or multiple conditions? How would the time complexity change?"

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