Raw queries when needed in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to execute a raw SQL query using Express with a database client.

Express

db.query([1], (err, result) => {
  if (err) throw err;
  res.send(result.rows);
});

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

Adb.execute('SELECT * FROM users')

BSELECT * FROM users

C"SELECT * FROM users"

Dquery('SELECT * FROM users')

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put the SQL query inside quotes.

Using incorrect method names like execute or query without context.

The raw SQL query must be a string passed to the query method. Option C correctly provides the SQL string.

2fill in blank

medium

Complete the code to safely insert a user name using parameterized raw query to avoid SQL injection.

Express

const sql = 'INSERT INTO users(name) VALUES($1)';
db.query(sql, [[1]], (err, res) => {
  if (err) throw err;
  console.log('User added');
});

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

AuserName

Busername

Cname

Dreq.body.name

Attempts:

3 left

💡 Hint

Common Mistakes

Passing variable names that are undefined in the context.

Not using parameterized queries and inserting values directly.

The user name comes from the request body, so req.body.name is the correct value to pass as parameter.

3fill in blank

hard

Fix the error in the raw query callback by completing the missing parameter to handle the result.

Express

db.query('SELECT * FROM products', (err, [1]) => {
  if (err) {
    console.error(err);
    return;
  }
  res.json([1].rows);
});

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

Aresult

Bresponse

Cdata

Doutput

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter names that do not match the result object.

Forgetting to use the result parameter to access rows.

The second parameter in the callback is commonly named result and contains the query result including rows.

4fill in blank

hard

Fill both blanks to create a raw query that updates a user's email by id using parameters.

Express

const sql = 'UPDATE users SET email = $1 WHERE id = $2';
db.query(sql, [[1], [2]], (err, res) => {
  if (err) throw err;
  res.send('Email updated');
});

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

Areq.body.email

Breq.params.id

CuserEmail

DuserId

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of parameters.

Using undefined variables instead of request data.

The email comes from req.body.email and the user id from req.params.id to safely update the record.

5fill in blank

hard

Fill all three blanks to write a raw query that deletes a user by id and logs the affected row count.

Express

const sql = 'DELETE FROM users WHERE id = $1';
db.query(sql, [[1]], (err, [2]) => {
  if (err) throw err;
  console.log('Deleted rows:', [3].rowCount);
});

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

Areq.params.userId

Bresult

Cres

Dreq.body.id

Attempts:

3 left

💡 Hint

Common Mistakes

Using request body instead of URL params for id.

Not using the correct result parameter to get rowCount.

The id to delete is from req.params.userId, the callback result parameter is named result, and result.rowCount gives the number of deleted rows.

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