ORDER BY single column in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the SQL clause ORDER BY do?

It sorts the rows returned by a query based on one or more columns, either in ascending or descending order.

beginner

How do you sort query results by a single column in ascending order?

Use ORDER BY column_name ASC. ASC means ascending order and is the default if not specified.

beginner

How do you sort query results by a single column in descending order?

Use ORDER BY column_name DESC. DESC means descending order.

beginner

What happens if you use ORDER BY without specifying ASC or DESC?

The results are sorted in ascending order by default.

intermediate

Can ORDER BY be used with columns not in the SELECT list?

Yes, you can order by any column in the table, even if it is not selected in the output.

Which SQL clause sorts the results by a single column?

A GROUP BY

B ORDER BY

C WHERE

D HAVING

ORDER BY sorts the query results by one or more columns.

What is the default sort order when using ORDER BY without ASC or DESC?

A Descending

B Random

C Ascending

D No sorting

By default, ORDER BY sorts in ascending order.

How do you sort results by the column age in descending order?

A ORDER BY age DESC

B ORDER BY age ASC

C ORDER BY DESC age

D SORT BY age DESC

The correct syntax is ORDER BY age DESC.

Can you use ORDER BY on a column not included in the SELECT statement?

A Only in MySQL

B No

C Only if the column is indexed

D Yes

You can order by any column in the table, even if it is not selected.

Which keyword sorts data from smallest to largest?

A ASC

B ORDER

C SORT

D DESC

ASC sorts data in ascending order (smallest to largest).

Explain how to sort query results by a single column in SQL.

Think about the clause that controls the order of rows.

What happens if you use ORDER BY on a column not included in the SELECT list?

Consider if the column must appear in the output to sort by it.

Practice

1. What does the SQL clause ORDER BY do when used with a single column?

easy

A. It deletes rows that have duplicate values in that column.

B. It filters the rows to only show those with unique values in that column.

C. It groups the rows by the values in that column.

D. It sorts the query results based on the values in that column.

Solution

1. Step 1: Understand the purpose of ORDER BY

   The ORDER BY clause is used to arrange the rows returned by a query in a specific order based on one or more columns.

2. Step 2: Focus on single column sorting

   When used with a single column, it sorts the results either ascending (default) or descending based on that column's values.

3. Final Answer:

   It sorts the query results based on the values in that column. -> Option D

4. Quick Check:

   ORDER BY = Sort results [OK]

Hint: ORDER BY arranges rows by column values [OK]

Common Mistakes:

• Confusing ORDER BY with filtering or grouping
• Thinking ORDER BY removes duplicates
• Assuming ORDER BY changes data in the table

2. Which of the following is the correct syntax to sort the table Employees by the column LastName in ascending order?

easy

A. SELECT * FROM Employees ORDER BY LastName DESC;

B. SELECT * FROM Employees SORT BY LastName;

C. SELECT * FROM Employees ORDER BY LastName ASC;

D. SELECT * FROM Employees ORDER LastName;

Solution

1. Step 1: Recall correct ORDER BY syntax

   The correct syntax to sort results is ORDER BY column_name. To specify ascending order, use ASC (which is also default).

2. Step 2: Check each option

   SELECT * FROM Employees ORDER BY LastName ASC; uses correct syntax with ORDER BY LastName ASC. SELECT * FROM Employees SORT BY LastName; uses invalid keyword SORT BY. SELECT * FROM Employees ORDER LastName; misses BY. SELECT * FROM Employees ORDER BY LastName DESC; sorts descending, not ascending.

3. Final Answer:

   SELECT * FROM Employees ORDER BY LastName ASC; -> Option C

4. Quick Check:

   ORDER BY + column + ASC = correct syntax [OK]

Hint: Use ORDER BY column ASC for ascending sort [OK]

Common Mistakes:

• Using SORT BY instead of ORDER BY
• Omitting BY keyword
• Confusing ASC with DESC

3. Given the table Products with columns ProductID and Price, what will be the order of ProductID after running this query?

SELECT ProductID FROM Products ORDER BY Price DESC;

Assume the data:
ProductID: 1, 2, 3
Price: 10, 30, 20

medium

A. [1, 3, 2]

B. [2, 3, 1]

C. [2, 1, 3]

D. [3, 2, 1]

Solution

1. Step 1: Understand ORDER BY Price DESC

   The query sorts rows by Price in descending order, so highest price first.

2. Step 2: Sort the data by Price descending

   Prices are 10 (ProductID 1), 30 (ProductID 2), 20 (ProductID 3). Descending order: 30, 20, 10. Corresponding ProductIDs: 2, 3, 1.

3. Final Answer:

   [2, 3, 1] -> Option B

4. Quick Check:

   Price DESC sorts highest to lowest [OK]

Hint: Sort by column DESC to get highest values first [OK]

Common Mistakes:

• Mixing ascending and descending order
• Sorting by ProductID instead of Price
• Assuming default ascending order

4. Identify the error in this SQL query:

SELECT Name FROM Customers ORDER LastName;

medium

A. Missing BY keyword after ORDER

B. ORDER BY cannot be used with SELECT

C. Name column does not exist

D. ORDER BY requires two columns

Solution

1. Step 1: Check ORDER BY syntax

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

2. Step 2: Verify other parts

   The SELECT statement is valid, and Name is assumed to exist. ORDER BY can be used with SELECT. Only one column is needed for ORDER BY.

3. Final Answer:

   Missing BY keyword after ORDER -> Option A

4. Quick Check:

   ORDER BY requires BY keyword [OK]

Hint: ORDER BY must include BY keyword [OK]

Common Mistakes:

• Omitting BY after ORDER
• Thinking ORDER BY needs multiple columns
• Assuming ORDER BY can't be used with SELECT

5. You have a table Students with columns StudentID, Name, and Score. You want to list all students ordered by their Score from highest to lowest, but if two students have the same score, order them alphabetically by Name. Which query correctly 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: Analyze each option

   SELECT * FROM Students ORDER BY Score DESC, Name ASC; orders by Score DESC then Name ASC, matching requirements. 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, wrong directions. SELECT * FROM Students ORDER BY Score DESC; only sorts by Score DESC, no tie-breaker.

3. Final Answer:

   SELECT * FROM Students ORDER BY Score DESC, Name ASC; -> Option A

4. Quick Check:

   ORDER BY primary DESC, secondary ASC for tie-break [OK]

Hint: Use ORDER BY primary DESC, secondary ASC for tie-breaks [OK]

Common Mistakes:

• Reversing sort order directions
• Not adding secondary column for tie-break
• Using only one column when two are needed