> ## Documentation Index
> Fetch the complete documentation index at: https://docs.clickml.app/llms.txt
> Use this file to discover all available pages before exploring further.

# Merge and Join DataFrames component

> Join two DataFrames on a shared key column using inner, left, right, or outer joins to combine related datasets before model training.

The **Merge / Join** component combines two DataFrames side-by-side by matching rows on one or more key columns — equivalent to a SQL JOIN.

## Configuration

| Option       | Description                                             | Default |
| ------------ | ------------------------------------------------------- | ------- |
| **How**      | Join type: `inner`, `left`, `right`, `outer`            | `inner` |
| **Left On**  | Key column(s) from the left DataFrame                   | —       |
| **Right On** | Key column(s) from the right DataFrame                  | —       |
| **Suffixes** | Suffix added to overlapping column names (e.g. `_x,_y`) | `_x,_y` |

### Join types

| Type  | Result                                                         |
| ----- | -------------------------------------------------------------- |
| inner | Only rows with matching keys in both DataFrames                |
| left  | All rows from the left DataFrame; NaN for unmatched right rows |
| right | All rows from the right DataFrame; NaN for unmatched left rows |
| outer | All rows from both DataFrames; NaN where no match              |

## Input / Output

|        | Type                             |
| ------ | -------------------------------- |
| Input  | Left DataFrame + Right DataFrame |
| Output | DataFrame                        |

<Note>
  Connect two separate data source components (CSV Reader, Excel Reader) to the left and right input handles of Merge / Join.
</Note>