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

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.

Workflow structure:

[HubSpot Node] ──────► [Merge Node] ──────► [Output]
                           ▲
[Postgres Node] ───────────┘
```text
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)   |

```json
// 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
}
```text
> **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](../code-node-mastery/01-flatten-deeply-nested-api-responses.md) | [Use the HTTP Request Node as a Universal Connector](../integration-patterns/01-use-the-http-request-node-as-a-universal-connector.md)