Raw queries when needed in Express - Step-by-Step Execution

Concept Flow - Raw queries when needed

Receive HTTP request

↓

Check if raw query needed?

No→Use ORM methods

Yes↓

Write raw SQL query string

↓

Send query to database

↓

Receive raw results

↓

Send response to client

This flow shows how Express handles a request that needs a raw SQL query instead of ORM methods.

Execution Sample

Express

app.get('/users', async (req, res) => {
  const result = await db.query('SELECT * FROM users WHERE age > $1', [30]);
  res.json(result.rows);
});

This code runs a raw SQL query to get users older than 30 and sends the results as JSON.

Execution Table

Step	Action	Query String	Parameters	Result	Response Sent
1	Receive GET /users request
2	Decide to run raw query	SELECT * FROM users WHERE age > $1	[30]
3	Send query to database	SELECT * FROM users WHERE age > $1	[30]	Rows with age > 30
4	Receive query results			Rows with age > 30
5	Send JSON response			Rows with age > 30	JSON array of users

💡 Response sent to client with raw query results

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
req	HTTP request object	HTTP request object	HTTP request object	HTTP request object	HTTP request object
queryString		SELECT * FROM users WHERE age > $1	SELECT * FROM users WHERE age > $1	SELECT * FROM users WHERE age > $1	SELECT * FROM users WHERE age > $1
params		[30]	[30]	[30]	[30]
result				Rows with age > 30	Rows with age > 30
res	HTTP response object	HTTP response object	HTTP response object	HTTP response object	Sent JSON response

Key Moments - 3 Insights

Why do we use raw queries instead of ORM methods sometimes?

Raw queries let us write custom SQL for complex or optimized operations that ORM methods can't easily do, as shown in step 2 of the execution_table.

How do parameters like [30] protect the query?

Parameters prevent SQL injection by separating data from code, as seen in the 'Parameters' column in steps 2 and 3.

What happens if the raw query returns no rows?

The result will be an empty array, and the response will send an empty JSON array, similar to step 5 but with no user data.

Visual Quiz - 3 Questions

Look at the execution_table, what is the query string sent to the database at step 3?

A SELECT * FROM users WHERE age > $1

B SELECT * FROM users

C INSERT INTO users VALUES ($1)

D UPDATE users SET age = $1

💡 Hint

Check the 'Query String' column at step 3 in the execution_table.

At which step does the server send the JSON response back to the client?

A Step 2

B Step 3

C Step 5

D Step 4

💡 Hint

Look at the 'Response Sent' column in the execution_table.

If the parameter changed from [30] to [50], how would the result change?

A It would return users younger than 30

B It would return users older than 50 instead of 30

C It would return all users regardless of age

D It would cause a syntax error

💡 Hint

Refer to the 'Parameters' column and how it affects the query in the execution_table.

Concept Snapshot

Raw queries in Express let you write SQL directly for complex database tasks.
Use parameterized queries to keep data safe from injection.
Send raw SQL with db.query(sql, params) and handle results manually.
Useful when ORM methods are too limited or slow.
Always send the query results back as a response to the client.

Full Transcript

This visual execution shows how Express handles raw SQL queries when needed. First, the server receives a request. It decides to run a raw SQL query instead of using ORM methods. The raw SQL string and parameters are prepared. The query is sent to the database. The database returns matching rows. Finally, the server sends these rows as a JSON response to the client. Variables like the query string, parameters, and results change step by step. Beginners often wonder why raw queries are used, how parameters protect queries, and what happens if no data is returned. The quiz questions help check understanding of query strings, response timing, and parameter effects.