Why Integer types (smallint, integer, bigint) in PostgreSQL? - Purpose & Use Cases

The Big Idea

What if your database could save space and avoid errors just by choosing the right number size automatically?

The Scenario

Imagine you are keeping track of the number of books in a library using a simple list on paper. You write down numbers without thinking about how big or small they might get.

Later, you realize some numbers are too big to fit in your small boxes, and some boxes are wasted because the numbers are tiny.

The Problem

Using the same size box for all numbers wastes space or causes errors when numbers are too big.

Manually guessing the right size for each number is slow and can lead to mistakes, like running out of space or using too much memory.

The Solution

Integer types like smallint, integer, and bigint let the database pick the right size box automatically.

This saves space and avoids errors by matching the number size to the right type.

Before vs After

✗ Before

CREATE TABLE books (count INTEGER); -- always uses 4 bytes

✓ After

CREATE TABLE books (count SMALLINT); -- uses 2 bytes for small numbers

What It Enables

Efficient storage and accurate handling of numbers of different sizes without wasting space or risking errors.

Real Life Example

A bank stores account balances: smallint for small accounts, integer for regular accounts, and bigint for very large balances, ensuring fast and safe data handling.

Key Takeaways

Integer types help match number size to storage space.

This prevents wasted space and errors from numbers too big or too small.

Choosing the right integer type improves database efficiency and reliability.

Practice

1. Which PostgreSQL integer type is best suited for storing very large whole numbers?

easy

A. bigint

B. smallint

C. integer

D. decimal

Solution

1. Step 1: Understand integer types and their sizes

   smallint stores small numbers, integer stores medium-sized numbers, and bigint stores very large numbers.

2. Step 2: Identify the type for very large whole numbers

   Since the question asks for very large whole numbers, bigint is the correct choice.

3. Final Answer:

   bigint -> Option A

4. Quick Check:

   Very large whole numbers = bigint [OK]

Hint: Biggest integer type is bigint for very large numbers [OK]

Common Mistakes:

• Confusing smallint with bigint
• Choosing decimal which is for decimals, not integers
• Picking integer which is medium size

2. Which of the following is the correct way to declare a column named age as a 2-byte integer in PostgreSQL?

easy

A. age INT2(2);

B. age INTEGER(2);

C. age BIGINT(2);

D. age SMALLINT;

Solution

1. Step 1: Recall PostgreSQL integer type syntax

   PostgreSQL uses SMALLINT for 2-byte integers. The syntax is simply column_name SMALLINT;.

2. Step 2: Evaluate each option

   age SMALLINT; uses correct syntax. The other options incorrectly use size in parentheses (like INT2(2), INTEGER(2), BIGINT(2)), which is invalid for integer types in PostgreSQL.

3. Final Answer:

   age SMALLINT; -> Option D

4. Quick Check:

   2-byte integer = SMALLINT syntax [OK]

Hint: Use SMALLINT keyword for 2-byte integers, no size in parentheses [OK]

Common Mistakes:

• Adding size in parentheses like INTEGER(2)
• Using BIGINT for small numbers
• Specifying size like INT2(2) for integer types

3. What will be the result of this PostgreSQL query?

CREATE TABLE test_numbers (num SMALLINT); INSERT INTO test_numbers VALUES (40000); SELECT * FROM test_numbers;

medium

A. 40000

B. Error: integer out of range

C. 0

D. NULL

Solution

1. Step 1: Understand SMALLINT range

   SMALLINT can store values from -32768 to 32767 only.

2. Step 2: Check inserted value against range

   40000 is greater than 32767, so inserting it causes an error.

3. Final Answer:

   Error: integer out of range -> Option B

4. Quick Check:

   40000 > SMALLINT max 32767 = error [OK]

Hint: Check value fits type range; else error occurs [OK]

Common Mistakes:

• Assuming value truncates silently
• Expecting 0 or NULL instead of error
• Confusing SMALLINT range with INTEGER

4. You wrote this table definition:

CREATE TABLE sales (id INTEGER, amount SMALLINT);

But when inserting a large amount like 40000, you get an error. How do you fix it?

medium

A. Change amount column type to INTEGER

B. Change id column type to SMALLINT

C. Insert smaller values only

D. Change amount column type to tinyint

Solution

1. Step 1: Identify cause of error

   Amount column is SMALLINT which maxes at 32767, so 40000 is too large.

2. Step 2: Choose appropriate type to hold 40000

   INTEGER can hold values up to 2,147,483,647, so changing amount to INTEGER fixes the error.

3. Final Answer:

   Change amount column type to INTEGER -> Option A

4. Quick Check:

   40000 fits INTEGER but not SMALLINT [OK]

Hint: Use INTEGER for values larger than 32767 [OK]

Common Mistakes:

• Changing unrelated column type
• Trying to insert smaller values only
• Choosing tinyint which is a MySQL type, not PostgreSQL

5. You need to store user IDs that can be very large numbers, possibly exceeding 2 billion. Which PostgreSQL integer type should you choose and why?

hard

A. smallint because it uses less storage

B. integer because it supports up to 2 billion

C. bigint because it supports numbers larger than 2 billion

D. serial because it auto-increments

Solution

1. Step 1: Understand size limits of integer types

   smallint max is 32767, integer max is about 2,147,483,647, bigint supports much larger numbers.

2. Step 2: Match requirement to type

   User IDs may exceed 2 billion, so integer is insufficient. bigint is needed to store larger values.

3. Final Answer:

   bigint because it supports numbers larger than 2 billion -> Option C

4. Quick Check:

   IDs > 2 billion need bigint [OK]

Hint: Use bigint for numbers larger than 2 billion [OK]

Common Mistakes:

• Choosing smallint for large IDs
• Assuming integer supports >2 billion
• Confusing serial with integer size