Where clause filtering in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to filter users with age greater than 18.

C Sharp (C#)

var adults = users.Where(u => u.Age [1] 18);

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

A>

B==

C<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' will select users younger than 18.

Using '==' will select only users exactly 18 years old.

The 'Where' clause filters users whose Age is greater than 18, so the operator should be '>'.

2fill in blank

medium

Complete the code to filter products with price less than or equal to 100.

C Sharp (C#)

var affordable = products.Where(p => p.Price [1] 100);

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

A<=

B==

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' or '>=' will select expensive products, not affordable ones.

Using '==' will select only products priced exactly 100.

The 'Where' clause filters products priced at 100 or less, so the operator should be '<='.

3fill in blank

hard

Fix the error in the code to filter orders with status 'Completed'.

C Sharp (C#)

var completedOrders = orders.Where(o => o.Status [1] "Completed");

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

A<

B!=

C==

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' selects orders not completed.

Using '>' or '<' does not work for string comparison here.

To filter orders with status exactly 'Completed', use the equality operator '=='.

4fill in blank

hard

Fill both blanks to filter employees older than 30 and in the 'Sales' department.

C Sharp (C#)

var salesTeam = employees.Where(e => e.Age [1] 30 && e.Department [2] "Sales");

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

A>

B==

C<

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' for age will select younger employees.

Using '!=' for department will exclude 'Sales' employees.

The filter selects employees older than 30 (using '>') and in the 'Sales' department (using '==').

5fill in blank

hard

Fill all three blanks to filter books published after 2000, with more than 300 pages, and author is 'Smith'.

C Sharp (C#)

var selectedBooks = books.Where(b => b.Year [1] 2000 && b.Pages [2] 300 && b.Author [3] "Smith");

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

A>

B==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' or '<' will select older books or fewer pages.

Using '!=' for author will exclude books by Smith.

The filter uses '>' for Year and Pages to select books after 2000 and with more than 300 pages, and '==' to match author 'Smith'.

Practice

1.

What does the WHERE clause do in a SQL query?

easy

A. Groups rows by a column

B. Filters rows based on a condition

C. Joins two tables together

D. Sorts the rows in ascending order

Solution

1. Step 1: Understand the purpose of WHERE clause

   The WHERE clause is used to select only rows that meet a specific condition.

2. Step 2: Compare with other SQL clauses

   Sorting is done by ORDER BY, joining by JOIN, grouping by GROUP BY, so WHERE is for filtering rows.

3. Final Answer:

   Filters rows based on a condition -> Option B

4. Quick Check:

   WHERE clause = filter rows [OK]

Hint: WHERE filters rows by condition, not sorting or joining [OK]

Common Mistakes:

• Confusing WHERE with ORDER BY
• Thinking WHERE joins tables
• Mixing WHERE with GROUP BY

2.

Which of the following is the correct syntax to filter rows where Age is greater than 30?

SELECT * FROM Users WHERE ___;

easy

A. Age > 30

B. Age = > 30

C. Age >> 30

D. Age >= 30

Solution

1. Step 1: Identify correct comparison operator

   The operator for 'greater than' is >, so 'Age > 30' is correct.

2. Step 2: Check other options for syntax errors

   'Age = > 30' and 'Age >> 30' are invalid syntax. 'Age >= 30' means 'greater or equal', not strictly greater.

3. Final Answer:

   Age > 30 -> Option A

4. Quick Check:

   Use > for greater than [OK]

Hint: Use > for greater than, >= for greater or equal [OK]

Common Mistakes:

• Using = > instead of >
• Using >> which is invalid
• Confusing > with >= operator

3.

Given the table Employees with columns Name and Salary, what rows will this query return?

SELECT Name FROM Employees WHERE Salary < 50000;

medium

A. Employees with salary less than 50000

B. Employees with salary greater than 50000

C. All employees regardless of salary

D. Employees with salary equal to 50000

Solution

1. Step 1: Understand the WHERE condition

   The condition Salary < 50000 means select rows where salary is less than 50000.

2. Step 2: Interpret the query result

   The query returns only the Name column for employees meeting that condition.

3. Final Answer:

   Employees with salary less than 50000 -> Option A

4. Quick Check:

   WHERE Salary < 50000 filters salaries below 50000 [OK]

Hint: Less than means <, so Salary < 50000 filters lower salaries [OK]

Common Mistakes:

• Confusing < with >
• Thinking it returns all employees
• Assuming it returns salary column too

4.

Identify the error in this query that tries to select users with age 18 or older:

SELECT * FROM Users WHERE Age => 18;

medium

A. WHERE clause cannot use numeric comparisons

B. Missing quotes around 18

C. The operator => is invalid; should be >= instead

D. SELECT * is not allowed with WHERE

Solution

1. Step 1: Check the comparison operator

   The operator => is not valid SQL syntax; the correct operator for 'greater or equal' is >=.

2. Step 2: Verify other parts of the query

   Numeric values like 18 do not need quotes, WHERE supports numeric comparisons, and SELECT * works with WHERE.

3. Final Answer:

   The operator => is invalid; should be >= instead -> Option C

4. Quick Check:

   Use >= for greater or equal, not => [OK]

Hint: Use >= for greater or equal, not => [OK]

Common Mistakes:

• Using => instead of >=
• Adding quotes around numbers
• Thinking WHERE can't compare numbers

5.

You want to select all products from a Products table where the Price is between 10 and 20 inclusive. Which WHERE clause is correct?

hard

A. Price BETWEEN 10 AND 20 EXCLUSIVE

B. Price > 10 AND Price < 20

C. Price >= 10 OR Price <= 20

D. Price >= 10 AND Price <= 20

Solution

1. Step 1: Understand inclusive range filtering

   Inclusive means including 10 and 20, so use >= and <= operators.

2. Step 2: Analyze each option

   Price > 10 AND Price < 20 excludes 10 and 20 (strictly greater and less). Price >= 10 OR Price <= 20 uses OR, which selects too many rows. Price BETWEEN 10 AND 20 EXCLUSIVE is invalid syntax.

3. Final Answer:

   Price >= 10 AND Price <= 20 -> Option D

4. Quick Check:

   Inclusive range uses >= and <= with AND [OK]

Hint: Use >= and <= with AND for inclusive ranges [OK]

Common Mistakes:

• Using > and < excludes boundary values
• Using OR instead of AND
• Trying invalid BETWEEN syntax