Join operations in Laravel - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to perform a basic inner join between 'users' and 'posts' tables.

Laravel

$users = DB::table('users')
    ->[1]('posts', 'users.id', '=', 'posts.user_id')
    ->get();

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

Ajoin

Bselect

Cwhere

DgroupBy

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'select' instead of 'join' will only choose columns, not combine tables.

Using 'where' will filter rows but not join tables.

The join method performs an inner join between tables.

2fill in blank

medium

Complete the code to perform a left join between 'users' and 'profiles' tables.

Laravel

$users = DB::table('users')
    ->[1]('profiles', 'users.id', '=', 'profiles.user_id')
    ->get();

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

Ajoin

BcrossJoin

CrightJoin

DleftJoin

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'join' will exclude users without profiles.

Using 'rightJoin' will include all profiles but not all users.

The leftJoin method returns all records from the left table and matched records from the right table.

3fill in blank

hard

Fix the error in the join condition to correctly join 'orders' and 'customers' tables.

Laravel

$orders = DB::table('orders')
    ->join('customers', 'orders.customer_id', [1], 'customers.id')
    ->get();

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

A==

B=

C===

D=>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' or '===' causes syntax errors in join conditions.

Using '=>' is for arrays, not join conditions.

The join condition uses a single equals sign '=' to compare columns.

4fill in blank

hard

Fill both blanks to perform a right join between 'products' and 'categories' tables with correct join condition.

Laravel

$products = DB::table('products')
    ->[1]('categories', 'products.category_id', [2], 'categories.id')
    ->get();

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

ArightJoin

BleftJoin

C=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'leftJoin' instead of 'rightJoin' changes the join direction.

Using '==' instead of '=' causes errors.

The rightJoin method is used for right joins, and '=' is the correct operator for join conditions.

5fill in blank

hard

Fill all three blanks to create a join with an additional where clause filtering 'status' in 'tasks' table.

Laravel

$tasks = DB::table('tasks')
    ->[1]('users', 'tasks.user_id', [2], 'users.id')
    ->where('tasks.status', [3])
    ->get();

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

Ajoin

B=

C'completed'

DleftJoin

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'leftJoin' changes the join type.

Using wrong operator in join condition causes errors.

Forgetting quotes around 'completed' causes syntax errors.

The code uses join with '=' for the join condition and filters tasks with status 'completed'.

Practice

1. What does the join method do in Laravel's query builder?

easy

A. Creates a new table by merging two tables.

B. Returns all rows from the first table regardless of matches.

C. Deletes rows from the joined tables.

D. Combines rows from two tables where matching columns exist (inner join).

Solution

1. Step 1: Understand the purpose of join

   The join method combines rows from two tables where the join condition matches, which is an inner join.

2. Step 2: Differentiate from other join types

   Unlike leftJoin, join excludes rows without matches in the second table.

3. Final Answer:

   Combines rows from two tables where matching columns exist (inner join). -> Option D

4. Quick Check:

   Join = Inner join [OK]

Hint: Join means only matching rows combined [OK]

Common Mistakes:

• Confusing join with leftJoin
• Thinking join deletes data
• Assuming join creates new tables

2. Which of the following is the correct syntax to perform an inner join between 'users' and 'posts' on 'users.id' and 'posts.user_id' in Laravel?

easy

A. $users = DB::table('users')->join('posts', 'users.id' == 'posts.user_id')->get();

B. $users = DB::table('users')->join('posts', 'users.id', 'posts.user_id')->get();

C. $users = DB::table('users')->join('posts', 'users.id', '=', 'posts.user_id')->get();

D. $users = DB::table('users')->join('posts')->on('users.id', '=', 'posts.user_id')->get();

Solution

1. Step 1: Check the join method parameters

   The correct join method requires four parameters: table, first column, operator, second column.

2. Step 2: Validate the syntax

   $users = DB::table('users')->join('posts', 'users.id', '=', 'posts.user_id')->get(); correctly uses join('posts', 'users.id', '=', 'posts.user_id'). Other options miss operator or use invalid syntax.

3. Final Answer:

   $users = DB::table('users')->join('posts', 'users.id', '=', 'posts.user_id')->get(); -> Option C

4. Quick Check:

   Join syntax needs 4 parameters [OK]

Hint: Join needs 4 parameters: table, col1, operator, col2 [OK]

Common Mistakes:

• Omitting the operator '='
• Using '==' inside join parameters
• Trying to use 'on' method instead of parameters

3. Given the following Laravel query, what will be the output if the 'users' table has 3 users and the 'posts' table has 2 posts linked to user IDs 1 and 2?

$results = DB::table('users')
    ->join('posts', 'users.id', '=', 'posts.user_id')
    ->select('users.name', 'posts.title')
    ->get();
return $results;

medium

A. A collection with 2 records showing user names and their post titles.

B. A collection with 3 records showing all users regardless of posts.

C. An empty collection because no posts match.

D. A syntax error due to missing join condition.

Solution

1. Step 1: Understand inner join behavior

   The join returns only rows where users.id matches posts.user_id, so only users with posts appear.

2. Step 2: Count matching rows

   Since 2 posts link to user IDs 1 and 2, the result will have 2 records with user names and post titles.

3. Final Answer:

   A collection with 2 records showing user names and their post titles. -> Option A

4. Quick Check:

   Inner join returns matching rows only [OK]

Hint: Inner join returns only matching rows count [OK]

Common Mistakes:

• Assuming all users appear with join
• Confusing join with leftJoin
• Expecting syntax error without reason

4. Identify the error in this Laravel join query:

$data = DB::table('users')
    ->join('posts', 'users.id', 'posts.user_id')
    ->get();

medium

A. Missing the operator '=' between columns in join method.

B. Using 'join' instead of 'leftJoin'.

C. Incorrect table name 'posts'.

D. Missing select() method before get().

Solution

1. Step 1: Check join method parameters

   The join method requires four parameters: table, first column, operator, second column.

2. Step 2: Identify missing operator

   In the query, the operator '=' is missing between 'users.id' and 'posts.user_id'.

3. Final Answer:

   Missing the operator '=' between columns in join method. -> Option A

4. Quick Check:

   Join needs operator '=' [OK]

Hint: Join needs '=' operator between columns [OK]

Common Mistakes:

• Omitting the operator parameter
• Confusing join and leftJoin usage
• Thinking select() is mandatory before get()

5. You want to get all users and their posts, but also include users who have no posts. Which Laravel join method should you use and how?

hard

A. Use rightJoin('posts', 'users.id', '=', 'posts.user_id') to include all users.

B. Use leftJoin('posts', 'users.id', '=', 'posts.user_id') to include all users.

C. Use join('posts', 'users.id', '=', 'posts.user_id') to include all users.

D. Use crossJoin('posts') to include all users.

Solution

1. Step 1: Understand join types for including unmatched rows

   To include all users even if they have no posts, a left join is needed.

2. Step 2: Apply leftJoin with correct columns

   Use leftJoin('posts', 'users.id', '=', 'posts.user_id') to keep all users and join posts where available.

3. Final Answer:

   Use leftJoin('posts', 'users.id', '=', 'posts.user_id') to include all users. -> Option B

4. Quick Check:

   Left join keeps all rows from first table [OK]

Hint: Left join keeps all first table rows [OK]

Common Mistakes:

• Using join instead of leftJoin
• Confusing rightJoin with leftJoin
• Using crossJoin which multiplies rows