Aggregates (count, sum, avg) in Laravel - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to count all users in the database.

Laravel

$count = User::[1]();

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

Asum

Bcount

Cavg

Dmax

Attempts:

3 left

💡 Hint

Common Mistakes

Using sum() instead of count()

Using avg() which calculates average

The count() method returns the total number of records.

2fill in blank

medium

Complete the code to get the total price of all orders.

Laravel

$total = Order::[1]('price');

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

Acount

Bmin

Csum

Davg

Attempts:

3 left

💡 Hint

Common Mistakes

Using count() which counts rows

Using avg() which calculates average

The sum('price') method adds all values in the price column.

3fill in blank

hard

Fix the error in the code to calculate the average age of users.

Laravel

$averageAge = User::[1]('age');

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

Asum

Bmax

Ccount

Davg

Attempts:

3 left

💡 Hint

Common Mistakes

Using sum() or count() instead of avg()

The avg('age') method calculates the average value of the age column.

4fill in blank

hard

Fill both blanks to count users older than 30.

Laravel

$count = User::where('age', [1], [2])->count();

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

A>

B<

C30

D25

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>'

Using wrong number like 25

The where('age', '>', 30) filters users older than 30, then count() counts them.

5fill in blank

hard

Fill all three blanks to get the average price of products cheaper than 100.

Laravel

$average = Product::where('price', [1], [2])->[3]('price');

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

A<

B100

Cavg

Dsum

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<'

Using sum() instead of avg()

The code filters products with price less than 100, then calculates the average price.

Practice

1. What does the count() method do in Laravel Eloquent?

easy

A. Returns the number of records matching the query

B. Calculates the sum of a column

C. Finds the average value of a column

D. Deletes all records in the table

Solution

1. Step 1: Understand the purpose of count()

   The count() method counts how many records match the query conditions.

2. Step 2: Compare with other aggregate methods

   Unlike sum() or avg(), count() returns a number of rows, not a calculation on column values.

3. Final Answer:

   Returns the number of records matching the query -> Option A

4. Quick Check:

   count() = number of records [OK]

Hint: count() counts rows, sum() and avg() work on columns [OK]

Common Mistakes:

• Confusing count() with sum() or avg()
• Thinking count() returns column values
• Assuming count() deletes records

2. Which of the following is the correct syntax to get the sum of the price column using Eloquent?

easy

A. Product::sum(['price']);

B. Product::sum(price);

C. Product->sum('price');

D. Product::sum('price');

Solution

1. Step 1: Identify correct method call syntax

   In Laravel Eloquent, static calls use double colon :: and column names must be strings in quotes.

2. Step 2: Check each option

   Product::sum('price'); uses Product::sum('price'); which is correct. Product::sum(price); misses quotes, C uses arrow on class, D passes array incorrectly.

3. Final Answer:

   Product::sum('price'); -> Option D

4. Quick Check:

   sum('column') needs quotes and :: [OK]

Hint: Use quotes around column name and :: for static call [OK]

Common Mistakes:

• Omitting quotes around column name
• Using -> instead of :: on model class
• Passing column name as array

3. Given the code:

$total = Order::where('status', 'completed')->sum('amount');

What does $total contain?

medium

A. The count of orders with status 'completed'

B. An error because sum() cannot be used with where()

C. The sum of 'amount' for orders with status 'completed'

D. The average 'amount' for all orders

Solution

1. Step 1: Understand the query filter

   The where('status', 'completed') filters orders to only those completed.

2. Step 2: Apply the sum aggregate

   The sum('amount') adds up the 'amount' values of the filtered orders.

3. Final Answer:

   The sum of 'amount' for orders with status 'completed' -> Option C

4. Quick Check:

   where() filters, sum() adds column values [OK]

Hint: where() filters rows, sum() adds column values of filtered rows [OK]

Common Mistakes:

• Thinking sum() returns count of rows
• Believing sum() cannot be chained with where()
• Confusing sum() with avg()

4. What is wrong with this code snippet?

$average = User::avg(age);

medium

A. avg() requires a second parameter

B. Missing quotes around the column name 'age'

C. avg() cannot be used on User model

D. Using avg() without where() causes error

Solution

1. Step 1: Check method parameter syntax

   The avg() method requires the column name as a string, so it must be quoted.

2. Step 2: Identify the error cause

   Without quotes, PHP treats age as a constant or variable, causing an error or unexpected behavior.

3. Final Answer:

   Missing quotes around the column name 'age' -> Option B

4. Quick Check:

   Column names must be strings in quotes [OK]

Hint: Always quote column names in aggregate methods [OK]

Common Mistakes:

• Omitting quotes around column names
• Thinking avg() needs multiple parameters
• Assuming avg() requires where()

5. You want to get the average price of products that are in stock (stock > 0). Which Eloquent query is correct?

hard

A. Product::where('stock', '>', 0)->avg('price');

B. Product::avg('price')->where('stock', '>', 0);

C. Product::where('stock', '>', 0)->sum('price') / Product::count();

D. Product::sum('price')->where('stock', '>', 0) / Product::count();

Solution

1. Step 1: Filter products with stock > 0

   The where('stock', '>', 0) filters only products that are in stock.

2. Step 2: Calculate average price of filtered products

   The avg('price') calculates the average price of those filtered products.

3. Step 3: Check other options for correctness

   Product::avg('price')->where('stock', '>', 0); calls avg() before where(), which is invalid. Manual calculations with sum divided by count do not filter correctly or mix sum and count improperly.

4. Final Answer:

   Product::where('stock', '>', 0)->avg('price'); -> Option A

5. Quick Check:

   Filter first, then aggregate [OK]

Hint: Chain where() before avg() to filter then calculate [OK]

Common Mistakes:

• Calling aggregate before where()
• Manually dividing sum by count without filtering
• Mixing sum() and avg() incorrectly