Raw expressions in Laravel - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of raw expression in a query builder

What will be the output SQL query generated by this Laravel query builder code?

Laravel

$query = DB::table('users')
    ->select(DB::raw('count(*) as user_count'))
    ->toSql();
echo $query;

A select count(*) as user_count from users

B select count(*) as user_count from `users`

C select count(*) user_count from `users`

D select count(*) from `users`

💡 Hint

Remember Laravel adds backticks around table names in the generated SQL.

Laravel's query builder wraps table names with backticks and preserves raw expressions as-is. So the raw count(*) as user_count remains unchanged, and the table name is backticked.

❓ component_behavior

intermediate

Effect of raw expressions on query bindings

Given this Laravel query, what will be the value of the bindings array after execution?

Laravel

$query = DB::table('orders')
    ->whereRaw('price > ?', [100])
    ->where('status', '=', 'paid');
$bindings = $query->getBindings();

A [100, 'paid']

B ['paid', 100]

C [100]

D ['paid']

💡 Hint

Bindings are collected in the order they appear in the query.

The whereRaw adds a binding for 100 first, then the where adds a binding for 'paid'. So the bindings array is [100, 'paid'].

🔧 Debug

advanced

Why does this raw expression cause a syntax error?

Consider this Laravel query: DB::table('products') ->select(DB::raw('SUM(price) AS total_price')) ->whereRaw('category = ?', 'electronics') ->get(); Why does this code cause an error?

A The DB::raw expression is missing parentheses around SUM(price)

B The table name 'products' must be wrapped in backticks in DB::table

C The select method cannot accept raw expressions

D The whereRaw method expects the second argument to be an array, not a string

💡 Hint

Check the expected argument types for whereRaw bindings.

whereRaw expects the bindings as an array. Passing a string causes a type error.

📝 Syntax

advanced

Correct syntax for raw order by clause

Which option correctly orders users by a raw expression that calculates length of the name?

Laravel

DB::table('users')->orderByRaw(???)->get();

A 'LENGTH(name) DESC'

B LENGTH(name) DESC

C ['LENGTH(name) DESC']

D DB::raw('LENGTH(name) DESC')

💡 Hint

orderByRaw expects a string with the raw SQL expression.

orderByRaw takes a string. Passing a bare expression or array causes errors.

🧠 Conceptual

expert

Understanding security risks with raw expressions

Which statement best explains the security risk when using raw expressions in Laravel queries?

A Using raw expressions disables all query logging in Laravel

B Raw expressions automatically sanitize all inputs to prevent SQL injection

C Raw expressions can introduce SQL injection if user input is concatenated directly without bindings

D Raw expressions prevent Laravel from caching query results

💡 Hint

Think about how raw SQL is handled compared to parameter binding.

Raw expressions bypass Laravel's query builder protections. If user input is concatenated directly, it can cause SQL injection.

Practice

1. What is the primary purpose of using DB::raw() in Laravel queries?

easy

A. To insert raw SQL expressions directly into the query builder

B. To automatically escape all user inputs

C. To convert Eloquent models into arrays

D. To cache query results for faster access

Solution

1. Step 1: Understand the role of DB::raw()

   DB::raw() allows you to write raw SQL expressions inside Laravel's query builder without modification.

2. Step 2: Compare with other options

   Options B, C, and D describe different Laravel features unrelated to raw SQL expressions.

3. Final Answer:

   To insert raw SQL expressions directly into the query builder -> Option A

4. Quick Check:

   DB::raw() = raw SQL insertion [OK]

Hint: DB::raw() means write SQL exactly as is inside queries [OK]

Common Mistakes:

• Thinking DB::raw() escapes inputs automatically
• Confusing DB::raw() with model conversion
• Assuming DB::raw() caches queries

2. Which of the following is the correct syntax to use DB::raw() in a Laravel query builder to select the current date?

easy

A. DB::table('users')->select(DB::raw('CURRENT_DATE'))->get();

B. DB::table('users')->select('CURRENT_DATE')->get();

C. DB::table('users')->selectRaw('CURRENT_DATE')->get();

D. DB::table('users')->selectRaw(DB::raw('CURRENT_DATE'))->get();

Solution

1. Step 1: Identify correct raw expression usage

   DB::raw() wraps the raw SQL string inside select() to insert it as is.

2. Step 2: Analyze other options

   DB::table('users')->select('CURRENT_DATE')->get(); treats 'CURRENT_DATE' as a column name, not raw SQL. DB::table('users')->selectRaw('CURRENT_DATE')->get(); uses selectRaw() correctly but without DB::raw(), which is valid but not the exact syntax asked. DB::table('users')->selectRaw(DB::raw('CURRENT_DATE'))->get(); nests DB::raw() inside selectRaw(), which is incorrect.

3. Final Answer:

   DB::table('users')->select(DB::raw('CURRENT_DATE'))->get(); -> Option A

4. Quick Check:

   Use DB::raw() inside select() for raw SQL [OK]

Hint: Use DB::raw('SQL') inside select() for raw SQL [OK]

Common Mistakes:

• Using select() with string instead of DB::raw()
• Confusing selectRaw() and DB::raw() usage
• Nesting DB::raw() inside selectRaw() incorrectly

3. What will be the output of the following Laravel query?

DB::table('orders')
  ->select('id', DB::raw('price * quantity AS total'))
  ->where('status', 'completed')
  ->get();

medium

A. An empty collection because raw expressions are not supported in where clauses

B. A syntax error because raw expressions cannot have aliases

C. A collection of orders with id and a calculated total price (price * quantity)

D. A collection with only id and price fields, ignoring quantity

Solution

1. Step 1: Understand the select with DB::raw()

   The query selects 'id' and a raw SQL expression calculating 'price * quantity' as 'total'. This is valid and returns those fields.

2. Step 2: Check the where clause and output

   The where clause filters orders with status 'completed'. The output is a collection of matching orders with 'id' and 'total' fields.

3. Final Answer:

   A collection of orders with id and a calculated total price (price * quantity) -> Option C

4. Quick Check:

   DB::raw() with alias returns calculated fields [OK]

Hint: DB::raw() can calculate fields with aliases in select [OK]

Common Mistakes:

• Thinking raw expressions cannot have aliases
• Assuming raw expressions affect where clause support
• Ignoring the calculated field in output

4. Identify the error in this Laravel query using raw expressions:

DB::table('users')
  ->where(DB::raw('LENGTH(name)'), '>', 5)
  ->get();

medium

A. Raw expressions cannot be used inside where clauses

B. The syntax is correct; no error present

C. DB::raw() should be wrapped inside a closure for where

D. The comparison operator '>' is invalid in this context

Solution

1. Step 1: Review usage of DB::raw() in where clause

   Using DB::raw() inside where to apply SQL functions like LENGTH() is valid syntax in Laravel.

2. Step 2: Check operators and syntax

   The '>' operator is valid for comparison. No wrapping closure is required here.

3. Final Answer:

   The syntax is correct; no error present -> Option B

4. Quick Check:

   DB::raw() works in where clauses with operators [OK]

Hint: DB::raw() can be used directly in where with operators [OK]

Common Mistakes:

• Assuming raw expressions are disallowed in where
• Thinking a closure is needed for DB::raw() in where
• Misunderstanding comparison operator validity

5. You want to update all users' scores by adding 10 points using a raw SQL expression in Laravel. Which code snippet correctly achieves this safely?

hard

A. DB::table('users')->update(DB::raw('score = score + 10'));

B. DB::table('users')->update(['score' => 'score + 10']);

C. DB::table('users')->updateRaw('score = score + 10');

D. DB::table('users')->update(['score' => DB::raw('score + 10')]);

Solution

1. Step 1: Understand how to update with raw expressions

   To update a column by adding a value, use DB::raw() inside the update array to write the SQL expression.

2. Step 2: Analyze each option

   DB::table('users')->update(['score' => DB::raw('score + 10')]); correctly uses DB::raw('score + 10') as the new value. DB::table('users')->update(['score' => 'score + 10']); treats it as a string, not SQL. DB::table('users')->update(DB::raw('score = score + 10')); passes DB::raw() directly to update(), which expects an array, causing error. DB::table('users')->updateRaw('score = score + 10'); uses a non-existent updateRaw() method.

3. Final Answer:

   DB::table('users')->update(['score' => DB::raw('score + 10')]); -> Option D

4. Quick Check:

   Use DB::raw() inside update array for calculations [OK]

Hint: Use DB::raw() inside update array for arithmetic updates [OK]

Common Mistakes:

• Passing raw SQL as string without DB::raw()
• Calling non-existent updateRaw() method
• Passing DB::raw() directly instead of in array