ORDER BY single column in MySQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this ORDER BY query?

Given the table Employees with columns id, name, and salary, what will be the order of name after running this query?

SELECT name FROM Employees ORDER BY salary ASC;

MySQL

CREATE TABLE Employees (id INT, name VARCHAR(20), salary INT);
INSERT INTO Employees VALUES (1, 'Alice', 5000), (2, 'Bob', 3000), (3, 'Charlie', 4000);

A ["Alice", "Charlie", "Bob"]

B ["Alice", "Bob", "Charlie"]

C ["Charlie", "Bob", "Alice"]

D ["Bob", "Charlie", "Alice"]

💡 Hint

ORDER BY salary ASC sorts salaries from smallest to largest.

The query orders employees by their salary in ascending order. Bob has the lowest salary (3000), then Charlie (4000), then Alice (5000).

📝 Syntax

intermediate

Which query has a syntax error in ORDER BY clause?

Identify the query that will cause a syntax error when ordering by a single column.

A SELECT * FROM Products ORDER BY;

B SELECT * FROM Products ORDER BY name ASC;

C SELECT * FROM Products ORDER BY price DESC;

D SELECT * FROM Products ORDER BY id;

💡 Hint

ORDER BY must be followed by a column name or expression.

Option A ends ORDER BY without specifying a column, causing a syntax error.

❓ optimization

advanced

Which query is most efficient to order by a single indexed column?

Assuming Orders table has an index on order_date, which query will best use the index to order results?

A SELECT * FROM Orders ORDER BY order_date DESC;

B SELECT * FROM Orders ORDER BY order_date ASC;

C SELECT * FROM Orders ORDER BY order_date + INTERVAL 1 DAY;

D SELECT * FROM Orders ORDER BY YEAR(order_date);

💡 Hint

Ordering by the indexed column directly is faster than using functions on it.

Ordering by order_date ASC uses the index efficiently. Using functions like YEAR() or arithmetic disables index usage.

🔧 Debug

advanced

Why does this ORDER BY query return unexpected results?

Given this query:

SELECT product_name FROM Products ORDER BY price;

Prices are stored as VARCHAR, not numeric. What is the cause of unexpected order?

A Prices are sorted as strings, so '100' comes before '20'.

B ORDER BY cannot sort VARCHAR columns.

C The query is missing ASC or DESC keyword.

D The table lacks a primary key causing order issues.

💡 Hint

Think about how strings are sorted compared to numbers.

VARCHAR columns sort lexicographically, so '100' is less than '20' because '1' < '2'.

🧠 Conceptual

expert

What is the effect of ORDER BY on query result without LIMIT?

Consider a table Customers with 1000 rows. What does ORDER BY last_name do when used without LIMIT?

A Returns rows in random order because LIMIT is missing.

B Returns only the first row sorted by last_name.

C Returns all rows sorted by last_name in ascending order.

D Returns rows sorted by last_name but only if an index exists.

💡 Hint

ORDER BY affects the order of all rows returned.

ORDER BY sorts the entire result set. Without LIMIT, all rows are returned sorted.

Practice

1. What does the ORDER BY clause do in a MySQL query?

easy

A. It sorts the query results by one or more columns.

B. It filters rows based on a condition.

C. It groups rows with the same values.

D. It limits the number of rows returned.

Solution

1. Step 1: Understand the purpose of ORDER BY

   The ORDER BY clause is used to sort the results of a query based on one or more columns.

2. Step 2: Compare with other clauses

   Filtering rows is done by WHERE, grouping by GROUP BY, and limiting rows by LIMIT. So, only sorting matches ORDER BY.

3. Final Answer:

   It sorts the query results by one or more columns. -> Option A

4. Quick Check:

   ORDER BY = Sort results [OK]

Hint: ORDER BY sorts rows; WHERE filters rows [OK]

Common Mistakes:

• Confusing ORDER BY with WHERE clause
• Thinking ORDER BY filters rows
• Mixing ORDER BY with GROUP BY

2. Which of the following is the correct syntax to sort the table employees by the column salary in descending order?

easy

A. SELECT * FROM employees ORDER BY salary DOWN;

B. SELECT * FROM employees SORT BY salary DESC;

C. SELECT * FROM employees ORDER salary DESC;

D. SELECT * FROM employees ORDER BY salary DESC;

Solution

1. Step 1: Recall correct ORDER BY syntax

   The correct syntax to sort results is ORDER BY column_name ASC|DESC. Here, DESC means descending order.

2. Step 2: Check each option

   SELECT * FROM employees ORDER BY salary DESC; uses correct syntax. Options B, C, and D use invalid keywords or syntax.

3. Final Answer:

   SELECT * FROM employees ORDER BY salary DESC; -> Option D

4. Quick Check:

   ORDER BY + DESC = correct syntax [OK]

Hint: Use ORDER BY column DESC for descending sort [OK]

Common Mistakes:

• Using SORT BY instead of ORDER BY
• Omitting BY after ORDER
• Using DOWN instead of DESC

3. Given the table products with columns id and price, what will be the order of id after running this query?

SELECT id FROM products ORDER BY price ASC;

Assume the data:
id: 1, price: 50
id: 2, price: 20
id: 3, price: 30

medium

A. [1, 3, 2]

B. [2, 3, 1]

C. [3, 2, 1]

D. [1, 2, 3]

Solution

1. Step 1: Understand ORDER BY price ASC

   The query sorts rows by price in ascending order (lowest to highest).

2. Step 2: Sort the data by price

   Prices sorted ascending: 20 (id 2), 30 (id 3), 50 (id 1). So the id order is [2, 3, 1].

3. Final Answer:

   [2, 3, 1] -> Option B

4. Quick Check:

   Sort by price ASC = [2, 3, 1] [OK]

Hint: Sort by column values ascending to find order [OK]

Common Mistakes:

• Confusing ASC with DESC order
• Sorting by id instead of price
• Ignoring the ORDER BY clause

4. Identify the error in this query:

SELECT name FROM customers ORDER salary DESC;

medium

A. ORDER BY must come before SELECT

B. DESC cannot be used with ORDER

C. Missing BY keyword after ORDER

D. Missing WHERE clause

Solution

1. Step 1: Check ORDER BY syntax

   The correct syntax requires the keyword BY after ORDER. The query uses ORDER salary DESC which is invalid.

2. Step 2: Confirm other parts are correct

   DESC is valid with ORDER BY. No WHERE clause is needed for sorting. ORDER BY comes after SELECT.

3. Final Answer:

   Missing BY keyword after ORDER -> Option C

4. Quick Check:

   ORDER BY needs BY keyword [OK]

Hint: Always write ORDER BY, not just ORDER [OK]

Common Mistakes:

• Omitting BY after ORDER
• Using ORDER before SELECT
• Confusing DESC usage

5. You have a table students with columns name and score. You want to list all students sorted by their score from highest to lowest, but if two students have the same score, sort those students alphabetically by name ascending. Which query achieves this?

hard

A. SELECT * FROM students ORDER BY score DESC, name ASC;

B. SELECT * FROM students ORDER BY name ASC, score DESC;

C. SELECT * FROM students ORDER BY score ASC, name DESC;

D. SELECT * FROM students ORDER BY score DESC;

Solution

1. Step 1: Understand sorting requirements

   Primary sort is by score descending (highest first). Secondary sort for ties is by name ascending (alphabetical).

2. Step 2: Match query with requirements

   SELECT * FROM students ORDER BY score DESC, name ASC; orders by score DESC then name ASC, matching the requirement. SELECT * FROM students ORDER BY name ASC, score DESC; reverses order priorities. SELECT * FROM students ORDER BY score ASC, name DESC; sorts score ascending and name descending, which is wrong. SELECT * FROM students ORDER BY score DESC; misses secondary sort.

3. Final Answer:

   SELECT * FROM students ORDER BY score DESC, name ASC; -> Option A

4. Quick Check:

   ORDER BY score DESC, name ASC = correct [OK]

Hint: Use multiple columns in ORDER BY for tie-breakers [OK]

Common Mistakes:

• Reversing sort order priorities
• Missing secondary sort column
• Using ASC when DESC needed