🚀 Data Science Roadmap 2026

📍 Phase 3: SQL for Data Science

📖 Topic 4 — LIMIT

LIMIT is used to control how many rows a SQL query returns.

It is especially useful when you want to see only the first few records, such as:

• Top 5 highest salaries

• Top 10 products by sales

• First 20 customers

• Latest 10 transactions

🔹 Basic Syntax

SELECT *
FROM employees
LIMIT 5;

This returns only 5 rows from the result.

🔹 LIMIT with ORDER BY

This is where LIMIT becomes especially powerful.

Suppose you want the 5 highest-paid employees:

SELECT employee_name, salary
FROM employees
ORDER BY salary DESC
LIMIT 5;

The logical idea is:

Filter → Sort → Take required number of rows

For example:

Salary
120000
110000
95000
90000
85000

Only the top 5 rows are returned.

🔹 LIMIT Without ORDER BY

You can write:

SELECT *
FROM employees
LIMIT 5;

But without ORDER BY, you should not assume these are the "first" or "top" 5 meaningful records.

The database does not guarantee a particular order unless you explicitly specify one.

So for analysis, this is usually better:

SELECT *
FROM employees
ORDER BY salary DESC
LIMIT 5;

🔹 LIMIT with WHERE

You can combine WHERE, ORDER BY, and LIMIT.

Example:

SELECT employee_name, salary
FROM employees
WHERE department = 'IT'
ORDER BY salary DESC
LIMIT 3;

This finds the 3 highest-paid employees in the IT department.

🔹 LIMIT for Top-N Analysis

Top-N queries are extremely common in data analysis.

Top 10 products by sales

SELECT product_name, sales
FROM products
ORDER BY sales DESC
LIMIT 10;

5 most recent transactions

SELECT transaction_id, transaction_date, amount
FROM transactions
ORDER BY transaction_date DESC
LIMIT 5;

3 cheapest products

SELECT product_name, price
FROM products
ORDER BY price ASC
LIMIT 3;

🔹 LIMIT with OFFSET

OFFSET allows you to skip a certain number of rows before returning results.

Example:

SELECT *
FROM employees
LIMIT 5 OFFSET 10;

This means:

Skip 10 rows

↓

Return the next 5 rows

This is commonly used for pagination.

For example:

• Page 1 → LIMIT 10 OFFSET 0

• Page 2 → LIMIT 10 OFFSET 10

• Page 3 → LIMIT 10 OFFSET 20

Syntax can vary between SQL databases, so always check the specific database you are using.

🔹 LIMIT vs TOP vs FETCH

Different SQL databases may use different syntax.

MySQL/PostgreSQL/SQLite commonly use:

LIMIT 5;

SQL Server commonly uses:

SELECT TOP 5 *
FROM employees;

Standard SQL also supports:

FETCH FIRST 5 ROWS ONLY;

The concept is the same: restrict the number of returned rows.

🔹 Real-World Data Science Example

Suppose an analyst wants to investigate the 10 largest customer transactions.

SELECT customer_id,
       transaction_id,
       amount
FROM transactions
ORDER BY amount DESC
LIMIT 10;

This can help identify:

• High-value transactions

• Potential anomalies

• Important customers

• Transactions requiring further investigation

🔹 Common Mistakes

Mistake 1 — Using LIMIT without sorting

SELECT *
FROM products
LIMIT 10;

This does not necessarily mean "10 best products."

For that:

ORDER BY sales DESC
LIMIT 10;

Mistake 2 — Using ASC when you need the highest values

Wrong:

ORDER BY salary ASC
LIMIT 5;

This returns the lowest salaries.

For the highest salaries: