How can I merge all executions from Input 1 into one for proper comparison in n8n?

Below is an explanation and some workarounds for your issue.

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What’s happening

The Merge node is designed to combine items from each input if they come within the same execution. When you send items from Input 1 in multiple executions (or batches), the node processes only the items coming in the first execution while ignoring the later ones. n8n does not natively buffer or combine separate executions for a single input within the Merge node.

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Native Behavior and Limitations

• The Merge node waits for data from each connected input during a single execution.
• If one branch (Input 1) produces multiple executions while the other (Input 2) arrives as a single execution, only the items from the first execution on Input 1 are paired against Input 2.
• There isn’t a built-in flag or mode on the Merge node that automatically aggregates separate executions into one.

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Recommended Workarounds

To achieve your goal of comparing all items from Input 1 with Input 2, you need to consolidate the items from Input 1 so that they reside in a single execution before reaching the Merge node. Here are two recommended approaches:

1. Consolidate Upstream (Preferred)

Modify your workflow upstream so that the node generating Input 1 emits a single execution rather than multiple executions. For example:

• Use a Function or Code Node in “Run Once” Mode:
  Adjust the node producing Input 1 to use $input.all() so that it gathers all items and then outputs a consolidated array in one execution. For example:

  JAVASCRIPTCopied
  // Place this code node right after your multiple executions or trigger them in a way
  // that all the items are waiting to be consolidated.
  const allItems = $input.all().flatMap(execution => execution.json);
  return allItems.map(item => ({ json: item }));

  This ensures that the Merge node receives all items from Input 1 in a single execution.

2. Use an Aggregation Node

If altering the upstream node isn’t feasible, you can use an aggregation node to combine the multiple executions:

• Aggregate Node:
  Use the Aggregate node to collect all items from Input 1 into one execution. Make sure all executions have time to complete before passing the result to the Merge node.

• Combination with a Wait or Split In Batches Node:
  Although you mentioned you already tried using a Function node with $input.all(), make sure the node doing the consolidation is set to “Run Once” for all incoming items. Wire the aggregated output to the Merge node so that both Input 1 and Input 2 data arrive as single executions.

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Final Comparison Using the Merge Node

Once you’ve consolidated Input 1 into a single execution, you can use the Merge node in “Remove Matches” mode to compare against Input 2. This configuration should output only the items from Input 1 that do not have a match in Input 2.

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Summary

There isn’t a native setting in the Merge node to combine separate executions. The best practice is to consolidate the items upstream (either by adjusting the producing node or by inserting an aggregation step) so that the Merge node receives a single execution with all items for proper comparison.

By ensuring both inputs are single executions, the Merge node in “Remove Matches” mode will work as expected.

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Hope this helps with structuring your workflow! If you have any further questions on how to implement any of the steps, let me know.