> For the complete documentation index, see [llms.txt](https://docs.flowiseai.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.flowiseai.com/integrations/llamaindex/engine/sub-question-query-engine.md).

# Sub-Question Query Engine

A query engine designed to solve problem of answering a complex query using multiple data sources. It first breaks down the complex query into sub questions for each relevant data source, then gather all the intermediate reponses and synthesizes a final response.

<figure><img src="/files/7ASrycAtL3X2u76sbKVI" alt=""><figcaption></figcaption></figure>

## Inputs

* Query Engine Tools
* Chat Model
* Embeddings
* [Response Synthesizer](/integrations/llamaindex/response-synthesizer.md)

## Parameters

| Name                    | Description                                                         |
| ----------------------- | ------------------------------------------------------------------- |
| Return Source Documents | To return citations/sources that were used to build up the response |

## Outputs

| Name                   | Description                   |
| ---------------------- | ----------------------------- |
| SubQuestionQueryEngine | Final node to return response |