Select queries in Laravel - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a basic select query

What will be the output of this Laravel Eloquent query if the users table has 3 records with names 'Alice', 'Bob', and 'Charlie'?

Laravel

$users = User::select('name')->get();
return $users->pluck('name')->toArray();

A ["Alice", "Bob", "Charlie"]

B [{"name": "Alice"}, {"name": "Bob"}, {"name": "Charlie"}]

C ["Alice Bob Charlie"]

D []

💡 Hint

Remember that pluck extracts the values of a single column into an array.

The select('name') limits the columns to 'name'. The get() returns a collection of User models with only the 'name' attribute. Using pluck('name') extracts the names into a simple array.

❓ component_behavior

intermediate

Behavior of select with multiple columns

Given this Laravel query, what will be the structure of each item in the returned collection?

Laravel

$users = User::select('id', 'email')->get();
return $users->first();

A An array with 'id' and 'email' keys

B An object with all user properties including 'id' and 'email'

C An object with only 'id' and 'email' properties

D A string containing 'id' and 'email'

💡 Hint

Selecting specific columns limits the attributes loaded on the model.

The select('id', 'email') tells Eloquent to only fetch those columns. The returned model instance will have only those attributes set.

📝 Syntax

advanced

Correct syntax for selecting with alias

Which option correctly selects the 'name' column as 'username' using Laravel's query builder?

A DB::table('users')->select(['name as username'])->get();

B DB::table('users')->select('name')->as('username')->get();

C DB::table('users')->select(DB::raw('name as username'))->get();

D DB::table('users')->select('name as username')->get();

💡 Hint

Column aliases can be specified directly like 'name as username' in select().

Laravel's query builder supports specifying aliases directly in the select() method using the syntax 'name as username'. This generates the proper SQL alias and returns objects with the aliased property.

🔧 Debug

advanced

Identify the error in this select query

What error will this Laravel query produce?

Laravel

$users = User::select('id', 'email')->where('name', '=', 'Alice')->get();
return $users->email;

A Error: Property 'email' does not exist on Collection

B Error: Undefined variable 'users'

C No error, returns email of first user

D Error: Missing semicolon

💡 Hint

Remember what type is returned by get() method.

The get() method returns a collection, not a single model. Accessing $users->email causes an error because the collection does not have an 'email' property.

🧠 Conceptual

expert

Effect of select on eager loading relationships

If you run this query, what will be the effect on the eager loaded 'posts' relationship?

Laravel

$users = User::select('id', 'name')->with('posts')->get();

A The 'posts' relationship will not load because select limits the whole query

B The 'posts' relationship will load all columns for posts as usual

C The 'posts' relationship will only load 'id' and 'name' columns from posts

D The query will throw an error because select conflicts with with()

💡 Hint

Eager loading runs separate queries for relationships.

The select('id', 'name') applies only to the main User query. The eager loaded 'posts' relationship runs its own query and loads all columns by default.