ASC and DESC direction in MySQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output order of this query?

Consider a table Employees with columns id, name, and salary. What will be the order of name in the result of this query?

SELECT name FROM Employees ORDER BY salary ASC;

MySQL

SELECT name FROM Employees ORDER BY salary ASC;

A Names ordered from lowest salary to highest salary

B Names in random order

C Names ordered alphabetically by name

D Names ordered from highest salary to lowest salary

💡 Hint

ASC means ascending order, from smallest to largest.

The ORDER BY clause with ASC sorts the rows by the salary column from the smallest value to the largest. So names appear in order of increasing salary.

❓ query_result

intermediate

What does DESC do in this query?

Given a table Products with columns product_id and price, what will be the order of product_id in this query?

SELECT product_id FROM Products ORDER BY price DESC;

MySQL

SELECT product_id FROM Products ORDER BY price DESC;

A Product IDs ordered from lowest price to highest price

B Product IDs ordered randomly

C Product IDs ordered by product_id ascending

D Product IDs ordered from highest price to lowest price

💡 Hint

DESC means descending order, from largest to smallest.

ORDER BY price DESC sorts the products by price from the highest value to the lowest. So product IDs appear in order of decreasing price.

📝 Syntax

advanced

Which query correctly orders by two columns with different directions?

You want to order a table Orders by customer_id ascending and then by order_date descending. Which query is correct?

A SELECT * FROM Orders ORDER BY customer_id, order_date DESC ASC;

B SELECT * FROM Orders ORDER BY customer_id ASC, order_date DESC;

C SELECT * FROM Orders ORDER BY customer_id DESC, order_date ASC;

D SELECT * FROM Orders ORDER BY customer_id ASC order_date DESC;

💡 Hint

Separate columns with commas and specify direction after each column.

Option B correctly orders by customer_id ascending and then order_date descending. Option B reverses directions. Option B has invalid syntax with DESC ASC. Option B misses a comma.

❓ optimization

advanced

How to optimize sorting large data with ASC and DESC?

You have a large table Sales with millions of rows. You often run:

SELECT * FROM Sales ORDER BY sale_date DESC;

What is the best way to optimize this query?

A Remove ORDER BY clause to speed up query

B Create an index on sale_date in ascending order

C Create an index on sale_date in descending order

D Use GROUP BY sale_date instead of ORDER BY

💡 Hint

Indexes help sorting if they match the order direction.

Creating an index on sale_date descending helps the database quickly retrieve rows in descending order without sorting all rows. Ascending index won't help for DESC order. Removing ORDER BY changes results. GROUP BY is for aggregation, not sorting.

🧠 Conceptual

expert

What is the result of mixing ASC and DESC in ORDER BY with NULL values?

Consider a table Items with a column price that contains some NULL values. What is the order of rows when running:

SELECT * FROM Items ORDER BY price ASC, name DESC;

Assuming default NULL sorting behavior in MySQL, where do NULL prices appear?

A Rows with NULL prices appear last, then prices in ascending order; names sorted descending within same price

B Rows with NULL prices appear first, then prices in ascending order; names sorted descending within same price

C Rows with NULL prices appear randomly mixed in the result

D Query causes an error because NULLs cannot be sorted with ASC and DESC

💡 Hint

MySQL sorts NULLs last by default in ascending order.

In MySQL, when ordering ascending, NULL values appear last. So rows with NULL price come after all non-NULL prices. Within same price, names are sorted descending. The query runs without error.

Practice

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

easy

A. Filters the data to show only ascending values

B. Sorts the data from largest to smallest or Z to A

C. Groups the data by ascending order

D. Sorts the data from smallest to largest or A to Z

Solution

1. Step 1: Understand the meaning of ASC in ORDER BY

   ASC stands for ascending order, which means sorting from smallest to largest or alphabetically from A to Z.

2. Step 2: Compare with other options

   DESC is for descending order, filtering and grouping are different SQL operations unrelated to ASC.

3. Final Answer:

   Sorts the data from smallest to largest or A to Z -> Option D

4. Quick Check:

   ASC = ascending order = smallest to largest [OK]

Hint: ASC means ascending order: smallest to largest [OK]

Common Mistakes:

• Confusing ASC with DESC
• Thinking ASC filters data
• Mixing sorting with grouping

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

easy

A. SELECT * FROM employees ORDER BY salary DESC;

B. SELECT * FROM employees ORDER BY salary ASC;

C. SELECT * FROM employees ORDER salary DESC;

D. SELECT * FROM employees SORT BY salary DESC;

Solution

1. Step 1: Identify correct ORDER BY syntax

   The correct syntax to sort results is using ORDER BY followed by the column name and then ASC or DESC.

2. Step 2: Check each option

   SELECT * FROM employees ORDER BY salary ASC; uses ASC, not DESC. SELECT * FROM employees ORDER salary DESC; misses BY keyword. SELECT * FROM employees SORT BY salary DESC; uses SORT BY which is invalid in MySQL. SELECT * FROM employees ORDER BY salary DESC; is correct.

3. Final Answer:

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

4. Quick Check:

   ORDER BY + column + DESC is correct syntax [OK]

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

Common Mistakes:

• Omitting BY after ORDER
• Using SORT BY instead of ORDER BY
• Mixing ASC and DESC keywords

3. Given the table products with column price, what will be the order of prices returned by this query?

SELECT price FROM products ORDER BY price DESC;

medium

A. Prices sorted randomly

B. Prices sorted from lowest to highest

C. Prices sorted from highest to lowest

D. Prices grouped by price value

Solution

1. Step 1: Analyze ORDER BY with DESC

   ORDER BY price DESC sorts the prices from the largest value to the smallest value.

2. Step 2: Eliminate other options

   Prices sorted from lowest to highest is ascending order, Prices sorted randomly is incorrect because ORDER BY sorts results, Prices grouped by price value is grouping which is unrelated.

3. Final Answer:

   Prices sorted from highest to lowest -> Option C

4. Quick Check:

   DESC means descending order = highest to lowest [OK]

Hint: DESC sorts from highest to lowest [OK]

Common Mistakes:

• Confusing DESC with ASC
• Expecting random order without ORDER BY
• Thinking ORDER BY groups data

4. Identify the error in this query that tries to sort students by age in descending order:

SELECT * FROM students ORDER age DESC;

medium

A. The table name students is invalid

B. Missing BY keyword after ORDER

C. ORDER BY should be replaced with SORT BY

D. DESC cannot be used with ORDER

Solution

1. Step 1: Check ORDER BY syntax

   The correct syntax requires ORDER BY, not just ORDER, before the column name.

2. Step 2: Validate other parts

   DESC is valid with ORDER BY. SORT BY is not valid in MySQL. Table name is valid as given.

3. Final Answer:

   Missing BY keyword after ORDER -> Option B

4. Quick Check:

   ORDER BY is required, not just ORDER [OK]

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

Common Mistakes:

• Omitting BY after ORDER
• Using SORT BY instead of ORDER BY
• Misunderstanding DESC usage

5. You want to list all orders sorted first by order_date ascending, then by total_amount descending. Which query correctly achieves this?

hard

A. SELECT * FROM orders ORDER BY order_date ASC, total_amount DESC;

B. SELECT * FROM orders ORDER BY order_date DESC, total_amount ASC;

C. SELECT * FROM orders ORDER BY total_amount DESC, order_date ASC;

D. SELECT * FROM orders ORDER BY total_amount ASC, order_date DESC;

Solution

1. Step 1: Understand multi-column ORDER BY

   ORDER BY can sort by multiple columns in sequence: first column sorts first, then second column breaks ties.

2. Step 2: Match sorting directions

   We want order_date ascending first, then total_amount descending. SELECT * FROM orders ORDER BY order_date ASC, total_amount DESC; matches this order and directions exactly.

3. Final Answer:

   SELECT * FROM orders ORDER BY order_date ASC, total_amount DESC; -> Option A

4. Quick Check:

   First ASC on order_date, then DESC on total_amount [OK]

Hint: List columns in ORDER BY with directions in desired priority [OK]

Common Mistakes:

• Swapping column order in ORDER BY
• Mixing ASC and DESC directions incorrectly
• Using DESC when ASC is needed and vice versa