Raw queries when needed in Express

Introduction

Sometimes you need to write your own database commands directly to do things that tools can't do easily.

When you want to run a special database command not supported by your usual tools.

When you need to optimize a query for speed and want full control.

When you want to use database-specific features or functions.

When your usual query builder can't express the query you need.

When debugging or testing raw SQL commands quickly.

Syntax

Express

const result = await db.raw('YOUR SQL QUERY HERE', [optionalParams]);

Use db.raw() to run raw SQL queries in Express with a database library like Knex.

You can pass parameters safely to avoid SQL injection by using placeholders and an array of values.

Examples

This runs a raw SQL query to get users older than 18.

Express

const users = await db.raw('SELECT * FROM users WHERE age > ?', [18]);

This runs a raw SQL query to count all orders.

Express

const count = await db.raw('SELECT COUNT(*) FROM orders');

This updates prices for all products in the 'books' category by increasing them 10%.

Express

const result = await db.raw('UPDATE products SET price = price * 1.1 WHERE category = ?', ['books']);

Sample Program

This Express app uses a raw SQL query to get users aged 18 or older from an in-memory SQLite database and returns them as JSON.

Express

import express from 'express';
import knex from 'knex';

const app = express();

const db = knex({
  client: 'sqlite3',
  connection: {
    filename: ':memory:'
  },
  useNullAsDefault: true
});

// Setup a simple table and data
await db.schema.createTable('users', table => {
  table.increments('id');
  table.string('name');
  table.integer('age');
});

await db('users').insert([
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: 17 },
  { name: 'Charlie', age: 30 }
]);

app.get('/adults', async (req, res) => {
  const adultsResult = await db.raw('SELECT name, age FROM users WHERE age >= ?', [18]);
  const adults = adultsResult.rows || adultsResult; // Adjust for different DB clients
  res.json(adults);
});

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

Important Notes

Always use parameter placeholders (?) and pass values as an array to avoid SQL injection risks.

Raw queries bypass some safety and convenience features, so use them only when necessary.

Check your database library's documentation for exact syntax and return formats of raw queries.

Summary

Raw queries let you write direct SQL commands when needed.

Use placeholders and parameters to keep queries safe.

Good for special cases where normal query builders can't help.

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