WITH clause syntax in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a WITH clause in SQL.

SQL

WITH [1] AS (SELECT * FROM employees)

Drag options to blanks, or click blank then click option'

Atemp_table

BSELECT

CFROM

DWHERE

Attempts:

3 left

💡 Hint

Common Mistakes

Using SQL keywords like SELECT or FROM as the name.

Leaving the name blank.

The WITH clause starts by naming a temporary result set. Here, temp_table is the name given.

2fill in blank

medium

Complete the code to select all columns from the WITH clause named temp_table.

SQL

WITH temp_table AS (SELECT id, name FROM employees) SELECT [1] FROM temp_table;

Drag options to blanks, or click blank then click option'

Aid

B*

Cname

Demployees

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting a single column instead of all columns.

Using the original table name instead of the WITH clause name.

Using * selects all columns from the temporary table temp_table.

3fill in blank

hard

Fix the error in the WITH clause by completing the missing keyword.

SQL

WITH temp_table [1] (SELECT id FROM employees) SELECT * FROM temp_table;

Drag options to blanks, or click blank then click option'

AFROM

BINTO

CWHERE

DAS

Attempts:

3 left

💡 Hint

Common Mistakes

Using FROM instead of AS.

Omitting the keyword entirely.

The keyword AS is required to define the temporary table in a WITH clause.

4fill in blank

hard

Fill both blanks to create two WITH clauses and select from the second.

SQL

WITH [1] AS (SELECT id FROM employees), [2] AS (SELECT id FROM departments) SELECT * FROM [2];

Drag options to blanks, or click blank then click option'

Aemp_ids

Bdept_ids

Cemployees

Ddepartments

Attempts:

3 left

💡 Hint

Common Mistakes

Using original table names instead of new names.

Mixing up the order of names.

The first WITH clause is named emp_ids, the second dept_ids. The SELECT uses the second name.

5fill in blank

hard

Fill all three blanks to create a WITH clause, filter rows, and select specific columns.

SQL

WITH filtered_emps AS (SELECT [1], [2] FROM employees WHERE salary [3] 50000) SELECT * FROM filtered_emps;

Drag options to blanks, or click blank then click option'

Aid

Bname

C>

Ddepartment

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting columns not in the table.

Using wrong comparison operators like '<' or '='.

The query selects id and name columns from employees where salary is greater than 50000.

Practice

1. What is the main purpose of the WITH clause in SQL?

easy

A. To create temporary named result sets called Common Table Expressions (CTEs)

B. To permanently store data in a new table

C. To delete rows from a table

D. To update values in a table

Solution

1. Step 1: Understand the role of WITH clause

   The WITH clause defines temporary named result sets called CTEs that exist only during query execution.

2. Step 2: Compare options with WITH clause purpose

   Options B, C, and D describe permanent or data modification actions, which are not the purpose of WITH.

3. Final Answer:

   To create temporary named result sets called Common Table Expressions (CTEs) -> Option A

4. Quick Check:

   WITH clause = Temporary named results [OK]

Hint: WITH clause defines temporary named queries [OK]

Common Mistakes:

• Thinking WITH creates permanent tables
• Confusing WITH with data modification commands
• Assuming WITH is used for deleting or updating data

2. Which of the following is the correct syntax to start a query using a single CTE named cte_example?

easy

A. CREATE cte_example AS (SELECT * FROM table_name); SELECT * FROM cte_example;

B. WITH (SELECT * FROM table_name) AS cte_example SELECT * FROM cte_example;

C. WITH cte_example AS (SELECT * FROM table_name) SELECT * FROM cte_example;

D. SELECT * FROM cte_example WITH (SELECT * FROM table_name);

Solution

1. Step 1: Recall correct WITH clause syntax

   The correct syntax is: WITH cte_name AS (subquery) followed by the main SELECT using cte_name.

2. Step 2: Check each option's syntax

   WITH cte_example AS (SELECT * FROM table_name) SELECT * FROM cte_example; matches the correct syntax. The other options misuse keywords or order.

3. Final Answer:

   WITH cte_example AS (SELECT * FROM table_name) SELECT * FROM cte_example; -> Option C

4. Quick Check:

   WITH cte_name AS (query) SELECT ... [OK]

Hint: WITH cte_name AS (query) SELECT ... is correct syntax [OK]

Common Mistakes:

• Using CREATE instead of WITH for CTE
• Placing AS after the subquery instead of after CTE name
• Misordering clauses in the query

3. Given the following SQL query, what will be the output?

WITH numbers AS (SELECT 1 AS num UNION ALL SELECT 2 UNION ALL SELECT 3) SELECT SUM(num) FROM numbers;

medium

A. 1

B. 3

C. Syntax error

D. 6

Solution

1. Step 1: Understand the CTE content

   The CTE named 'numbers' contains rows with values 1, 2, and 3.

2. Step 2: Calculate the SUM of num column

   Sum of 1 + 2 + 3 equals 6.

3. Final Answer:

   6 -> Option D

4. Quick Check:

   1 + 2 + 3 = 6 [OK]

Hint: Sum values inside CTE to get result [OK]

Common Mistakes:

• Assuming UNION ALL removes duplicates
• Confusing SUM with COUNT
• Expecting syntax error due to CTE

4. Identify the error in this SQL query using a CTE:

WITH cte1 AS SELECT * FROM employees SELECT * FROM cte1;

medium

A. CTE name cannot be cte1

B. Missing parentheses around the CTE's SELECT statement

C. SELECT * FROM cte1 should come before WITH clause

D. WITH clause cannot be used with SELECT

Solution

1. Step 1: Check CTE syntax

   The CTE definition must have parentheses around the SELECT query: AS (SELECT ...)

2. Step 2: Identify missing parentheses

   The query misses parentheses after AS, causing syntax error.

3. Final Answer:

   Missing parentheses around the CTE's SELECT statement -> Option B

4. Quick Check:

   CTE query must be in parentheses [OK]

Hint: Always put CTE query inside parentheses after AS [OK]

Common Mistakes:

• Omitting parentheses around CTE query
• Placing main SELECT before WITH clause
• Thinking CTE names have restrictions beyond naming rules

5. Consider this SQL query using multiple CTEs:

WITH cte1 AS (SELECT id, salary FROM employees WHERE department = 'Sales'), cte2 AS (SELECT id, bonus FROM bonuses) SELECT cte1.id, cte1.salary, cte2.bonus FROM cte1 LEFT JOIN cte2 ON cte1.id = cte2.id;

What is the purpose of using multiple CTEs here?

hard

A. To organize complex queries by separating filtering and joining steps

B. To permanently store intermediate results in the database

C. To speed up query execution by caching results automatically

D. To avoid using JOINs by combining data in CTEs

Solution

1. Step 1: Analyze the role of each CTE

   cte1 filters employees in Sales with id and salary; cte2 selects bonuses by id.

2. Step 2: Understand the main query usage

   The main query joins these CTEs to combine salary and bonus data for Sales employees.

3. Step 3: Identify why multiple CTEs are used

   Using multiple CTEs organizes the query into clear steps: filtering and joining, improving readability.

4. Final Answer:

   To organize complex queries by separating filtering and joining steps -> Option A

5. Quick Check:

   Multiple CTEs = Organize complex queries [OK]

Hint: Use multiple CTEs to break complex queries into parts [OK]

Common Mistakes:

• Thinking CTEs store data permanently
• Assuming CTEs automatically speed up queries
• Believing CTEs replace JOINs entirely