Query optimization in Laravel - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all users with active status using Eloquent.

Laravel

$users = User::where('status', [1])->get();

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

A'pending'

B'deleted'

C'inactive'

D'active'

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong status string like 'inactive' or 'pending'.

We want to get users whose status is 'active', so the correct value is 'active'.

2fill in blank

medium

Complete the code to eager load the 'posts' relationship to optimize queries.

Laravel

$users = User::with([1])->get();

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

A'posts'

B'followers'

C'likes'

D'comments'

Attempts:

3 left

💡 Hint

Common Mistakes

Loading unrelated relationships like 'comments' or 'likes'.

Eager loading 'posts' reduces the number of queries when accessing user posts.

3fill in blank

hard

Fix the error in the query to count users with more than 5 posts.

Laravel

$count = User::has('posts', '>', [1])->count();

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

A1

B5

C10

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong number like 3 or 10 which changes the condition.

The condition requires counting users with more than 5 posts, so the number is 5.

4fill in blank

hard

Fill both blanks to optimize the query by selecting only 'id' and 'name' columns.

Laravel

$users = User::select([1], [2])->get();

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

A'id'

B'email'

C'name'

D'password'

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting 'email' or 'password' which are not needed here.

Selecting only 'id' and 'name' reduces data load and speeds up the query.

5fill in blank

hard

Fill all three blanks to build a query that filters users by age, orders by name, and limits results.

Laravel

$users = User::where('age', '>', [1])->orderBy([2], [3])->get();

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

A18

B'name'

C'asc'

D'desc'

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong age number or ordering direction.

This query gets users older than 18, orders them by name ascending, and retrieves the results.

Practice

1. What is the main benefit of using eager loading in Laravel queries?

easy

A. It reduces the number of database queries by loading related data upfront.

B. It automatically caches all query results for faster access.

C. It encrypts the query results for security.

D. It sorts the query results alphabetically.

Solution

1. Step 1: Understand eager loading purpose

   Eager loading loads related data in one query instead of many separate queries.

2. Step 2: Identify benefit in query optimization

   By reducing the number of queries, it speeds up the app and lowers database load.

3. Final Answer:

   It reduces the number of database queries by loading related data upfront. -> Option A

4. Quick Check:

   Eager loading = fewer queries [OK]

Hint: Eager loading means load related data once, not many times [OK]

Common Mistakes:

• Confusing eager loading with caching
• Thinking it sorts or encrypts data
• Believing it loads data lazily

2. Which of the following is the correct way to select only the 'name' and 'email' columns from the users table in Laravel?

easy

A. $users = DB::table('users')->select('name', 'email')->get();

B. $users = DB::table('users')->columns('name', 'email')->fetch();

C. $users = DB::table('users')->only('name', 'email')->all();

D. $users = DB::table('users')->pick('name', 'email')->fetchAll();

Solution

1. Step 1: Recall Laravel query builder syntax

   The method to specify columns is select(), and to get results is get().

2. Step 2: Match correct syntax

   $users = DB::table('users')->select('name', 'email')->get(); uses select('name', 'email')->get(), which is correct Laravel syntax.

3. Final Answer:

   $users = DB::table('users')->select('name', 'email')->get(); -> Option A

4. Quick Check:

   Select columns = select() + get() [OK]

Hint: Use select() to pick columns, then get() to fetch [OK]

Common Mistakes:

• Using non-existent methods like columns() or only()
• Confusing fetch() with get()
• Trying to fetch all columns without select()

3. Given the code below, what will be the number of queries executed?

Post::with('comments')->where('status', 'published')->get();

medium

A. 1 query

B. Number of comments queries

C. Number of posts + 1 queries

D. 2 queries

Solution

1. Step 1: Understand eager loading with 'with'

   The with('comments') loads related comments in a separate query.

2. Step 2: Count queries executed

   One query fetches posts with status 'published', second query fetches all related comments.

3. Final Answer:

   2 queries -> Option D

4. Quick Check:

   with() = 2 queries [OK]

Hint: with() runs 2 queries: main + related data [OK]

Common Mistakes:

• Thinking with() runs only 1 query
• Assuming one query per post for comments
• Confusing with() with lazy loading

4. Identify the problem in this Laravel query that causes slow performance:

$users = User::all();
foreach ($users as $user) {
  echo $user->profile->bio;
}

medium

A. The profile relation does not exist in User model.

B. The foreach loop syntax is incorrect.

C. Using all() loads all users without eager loading profiles, causing N+1 queries.

D. Using echo inside loop slows down PHP execution.

Solution

1. Step 1: Analyze query and loop

   User::all() loads all users but does not load related profiles eagerly.

2. Step 2: Identify N+1 query problem

   Accessing $user->profile inside loop triggers one query per user, causing many queries.

3. Final Answer:

   Using all() loads all users without eager loading profiles, causing N+1 queries. -> Option C

4. Quick Check:

   all() without eager loading = N+1 queries [OK]

Hint: Use with('profile') to avoid N+1 queries [OK]

Common Mistakes:

• Blaming loop syntax instead of query
• Assuming profile relation missing without checking
• Thinking echo slows query performance

5. You want to optimize a query that fetches posts with their authors and comments, but only need the post title, author name, and comment content. Which approach is best?

hard

A. Run separate queries for posts, authors, and comments and merge results in PHP.

B. Use eager loading with select() on posts, authors, and comments to fetch only needed columns.

C. Use lazy loading to fetch authors and comments only when accessed.

D. Fetch all posts, authors, and comments without filtering columns to avoid missing data.

Solution

1. Step 1: Understand data needed

   Only post title, author name, and comment content are required, so select only these columns.

2. Step 2: Apply eager loading with column selection

   Use with() to eager load authors and comments, and select() to limit columns for optimization.

3. Final Answer:

   Use eager loading with select() on posts, authors, and comments to fetch only needed columns. -> Option B

4. Quick Check:

   Eager load + select columns = best optimization [OK]

Hint: Combine eager loading and select() to fetch only needed data [OK]

Common Mistakes:

• Fetching all columns wastes resources
• Using lazy loading causes many queries
• Merging in PHP is slower than optimized queries