Merge

Join two lists of items into one, pairing items that match.

What it does

Merge has two inputs. It waits for both, then pairs each item from the first input (A) with the items from the second input (B) that satisfy your Match Keys, and combines each pair into one item.

Each match key compares a field on the A side with a field on the B side, with an operator (for example Is Equal To). Several keys can be linked with AND or OR. With no match keys, every A item pairs with every B item.

When both items have a field with the same name but different values, the result keeps both, renamed left-<field> and right-<field>. Fields with equal values are kept once.

Mode decides what happens to items that find no partner:

Mode	Result
Inner Join	Only matched pairs.
Left Join	Every A item: merged with its matches, or on its own when it has none.
Right Join	Every B item: merged with its matches, or on its own when it has none.
Left Outer Join	Same result as Left Join.
Right Outer Join	Same result as Right Join.

When to use it

• Add details from one source to another: contacts from a sheet plus their latest orders from an API, matched on email.
• Keep only the records present in both lists (Inner Join).

Merge does not wait for “whichever branch finishes first”. For that, use Funnel. To find what is new, gone or changed between two lists, use Compare Datasets.

Inputs and settings

Setting	Type	What it does
Mode REQ(required)	Choice	The mode to use for merging the inputs. Options: Inner Join, Left Join, Right Join, Left Outer Join, Right Outer Join. Default: Inner Join
Match Keys REQ(required)	Key mapping	The keys to use for matching the inputs.

Outputs

• Output

Dependencies and credentials

None. This node needs no connection and has no slots for other nodes.

Example workflow

1. Google Sheets reads your customer list (input A).
2. Http Request fetches recent orders (input B).
3. Merge in Left Join mode, with the match key A email Is Equal To B customerEmail.
4. Every customer comes out once per matching order, or once on their own when they have no order.

Common issues

• Nothing comes out. In Inner Join mode no pair matched. Check that both fields hold the same kind of value (for example both lower-case emails) and that the field names are spelled as they appear in the data.
• Many more items than expected. One A item matched several B items, and each pair becomes an item. Remove duplicates on B first, or add another match key.
• Fields called left-… and right-… appear. Both sides had a field with that name and different values. Rename one side first with Rename Keys if you want to keep a single field.

Related nodes

• Compare Datasets: sort two lists into new, gone, unchanged and changed.
• Funnel: continue when any one branch completes.
• Aggregate: gather items into one list.
• IF: split one stream into two.