Raw queries when needed in Express - Performance & Optimization

Performance: Raw queries when needed

MEDIUM IMPACT

Using raw queries affects server response time and database query execution speed, impacting how fast data is sent to the client.

Fetching complex data efficiently from the database

Express

await sequelize.query("SELECT users.*, orders.* FROM users JOIN orders ON users.id = orders.user_id WHERE orders.status = 'pending'");

Raw query executes a single optimized SQL statement reducing overhead and speeding up data retrieval.

📈 Performance Gainreduces query time by 30-50% and server blocking time

Fetching complex data efficiently from the database

Express

await User.findAll({ include: [{ model: Order, where: { status: 'pending' } }] });

ORM generates multiple queries or inefficient joins causing slower response and higher CPU usage.

📉 Performance Costblocks server response for 100-200ms on complex joins

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
ORM complex queries	N/A	N/A	Higher server response delay	[X] Bad
Raw SQL queries	N/A	N/A	Lower server response delay	[OK] Good

Rendering Pipeline

Raw queries reduce server processing time, allowing faster data delivery to the browser, improving initial content paint.

→Server Processing

→Network Transfer

→Browser Rendering

⚠️ BottleneckServer Processing due to ORM overhead

Core Web Vital Affected

LCP

Using raw queries affects server response time and database query execution speed, impacting how fast data is sent to the client.

Optimization Tips

1Use raw queries for complex or performance-critical database operations.

2Always sanitize inputs in raw queries to prevent SQL injection.

3Avoid raw queries for simple CRUD operations where ORM is efficient.

Performance Quiz - 3 Questions

Why might raw SQL queries improve performance over ORM methods?

A They reduce server CPU usage by avoiding ORM overhead

B They increase the number of database queries

C They add extra parsing steps on the server

D They always cache data automatically

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, and inspect the time taken for API calls fetching data.

What to look for: Look for shorter server response times and faster data transfer indicating efficient queries.

Practice

1. What is the main reason to use raw queries in Express applications?

easy

A. To write direct SQL commands when query builders are insufficient

B. To automatically generate SQL queries without any code

C. To avoid using any SQL and rely only on JavaScript

D. To speed up the server by skipping database calls

Solution

1. Step 1: Understand raw queries purpose

   Raw queries allow writing direct SQL commands for complex or special cases.

2. Step 2: Compare with other options

   Options A, B, and C are incorrect because raw queries do not skip database calls, auto-generate SQL, or avoid SQL.

3. Final Answer:

   To write direct SQL commands when query builders are insufficient -> Option A

4. Quick Check:

   Raw queries = direct SQL use [OK]

Hint: Raw queries = direct SQL for special cases [OK]

Common Mistakes:

• Thinking raw queries auto-generate SQL
• Believing raw queries avoid SQL entirely
• Assuming raw queries skip database calls

2. Which of the following is the correct way to use a raw query with parameters in Express using a SQL library?

easy

A. db.query('SELECT * FROM users WHERE id = ' + userId)

B. db.query('SELECT * FROM users WHERE id = ?', [userId])

C. db.query('SELECT * FROM users WHERE id = $userId')

D. db.query('SELECT * FROM users WHERE id = :userId')

Solution

1. Step 1: Identify parameterized query syntax

   Using '?' with an array of parameters is the standard safe way to pass values.

2. Step 2: Check other options

   db.query('SELECT * FROM users WHERE id = ' + userId) concatenates strings (unsafe). Options C and D use placeholders not standard in many Express SQL libraries.

3. Final Answer:

   db.query('SELECT * FROM users WHERE id = ?', [userId]) -> Option B

4. Quick Check:

   Use '?' + params array for safe raw queries [OK]

Hint: Use '?' with array for parameters in raw queries [OK]

Common Mistakes:

• Concatenating variables directly into query strings
• Using unsupported placeholder syntax
• Not passing parameters as an array

3. Given the code snippet:

const result = await db.query('SELECT * FROM products WHERE price > ?', [100]);
console.log(result.rows.length);

What will be logged if there are 5 products priced over 100?

medium

A. 5

B. undefined

C. 0

D. An error will occur

Solution

1. Step 1: Understand the query and parameters

   The raw query selects products with price greater than 100, passing 100 safely as a parameter.

2. Step 2: Interpret the result object

   Assuming the database library returns an object with a 'rows' array, its length will be the number of matching products, which is 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   Rows length = number of matching products [OK]

Hint: Result rows length = count of matched records [OK]

Common Mistakes:

• Expecting result directly as array without .rows
• Confusing parameter placement
• Assuming query returns undefined or error

4. Identify the error in this raw query usage:

const userId = 10;
const result = await db.query('SELECT * FROM users WHERE id = ' + userId);

medium

A. The parameter should be passed as an object, not concatenated

B. The query syntax is invalid because of missing quotes

C. It risks SQL injection by concatenating variables directly

D. The query will always return zero results

Solution

1. Step 1: Analyze query construction

   The query concatenates userId directly into the string, which is unsafe and can cause SQL injection.

2. Step 2: Understand best practice

   Parameters should be passed separately using placeholders to avoid injection risks.

3. Final Answer:

   It risks SQL injection by concatenating variables directly -> Option C

4. Quick Check:

   Never concatenate variables directly in raw queries [OK]

Hint: Avoid string concatenation; use placeholders [OK]

Common Mistakes:

• Ignoring SQL injection risks
• Thinking concatenation is safe for numbers
• Not using parameterized queries

5. You need to update multiple user records with different emails using raw queries in Express. Which approach is best to safely perform this?

hard

A. Use raw queries without parameters for faster execution

B. Concatenate all updates into one big query string and run once

C. Update users one by one by concatenating values directly

D. Use a loop with parameterized raw queries for each user update

Solution

1. Step 1: Consider safety and flexibility

   Using a loop with parameterized queries ensures each update is safe and avoids SQL injection.

2. Step 2: Evaluate other options

   Concatenating all updates risks injection and syntax errors; skipping parameters is unsafe; direct concatenation is insecure.

3. Final Answer:

   Use a loop with parameterized raw queries for each user update -> Option D

4. Quick Check:

   Loop + parameters = safe batch updates [OK]

Hint: Loop with parameters for multiple safe updates [OK]

Common Mistakes:

• Trying to build one big concatenated query
• Ignoring parameterization for speed
• Concatenating user data directly