Use the Merge Node's Combine Mode with Key Matching to Join Data

Use the Merge node in Combine, Merge By Fields mode to join two n8n data streams like a SQL JOIN. Set the key field for each input, choose whether to keep only matches or everything, and pick clash handling for overlapping fields. It enriches records from one source with data from another and replaces a complex Code node full of nested loops.

What does the Merge node's Combine mode do?

The Merge node in Combine > Merge By Fields mode performs the equivalent of a SQL JOIN between two n8n data streams. This is essential whenever you need to enrich records from one source with data from another.

Real-world example: Input 1 contains customer records from your CRM (HubSpot). Input 2 contains recent order data from your database. You want to merge them on email to produce an enriched customer record.

How do you configure Merge By Fields to join data?

Workflow structure:

[HubSpot Node] ──────► [Merge Node] ──────► [Output]
                           ▲
[Postgres Node] ───────────┘

Configure the Merge node:

Setting	Value
Mode	Combine
Combination Mode	Merge By Fields
Input 1 Field	email
Input 2 Field	customer_email
Output Type	Keep Matches
Clash Handling	Prefer Input 2 (order data wins)

// Input 1 (HubSpot) item:
{ "email": "jane@acme.com", "name": "Jane Doe", "lifecycle_stage": "customer" }

// Input 2 (Postgres) item:
{ "customer_email": "jane@acme.com", "last_order_date": "2025-03-15", "total_spent": 4250.00 }

// Merged output:
{
  "email": "jane@acme.com",
  "name": "Jane Doe",
  "lifecycle_stage": "customer",
  "last_order_date": "2025-03-15",
  "total_spent": 4250.00
}

Note: Handling Unmatched Records. Set Output Type to Keep Everything if you want to include customers who have no orders (a LEFT JOIN equivalent). Unmatched fields will be null.

This replaces what would otherwise be a complex Code node with nested loops and is significantly easier to maintain.

Related: Flatten Deeply Nested API Responses · Use the HTTP Request Node as a Universal Connector