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

# Link

> Create relationships between tables and select records from another table in the current record.

The Link field connects two tables. With a Link field, you can select records from another table in the current table and open the linked records when needed. Link fields are also required before you can use **Lookup** and **Rollup** fields.

## Use Cases

| Scenario                      | Good for                                                                            |
| ----------------------------- | ----------------------------------------------------------------------------------- |
| Customers and orders          | Link customers in the orders table, and view related orders from the customer table |
| Projects and tasks            | Link a task to its project, and view all tasks under a project                      |
| Students and courses          | Track course enrollment, project members, or other many-to-many relationships       |
| Line items and parent records | Link order line items to an order, then look up prices or roll up totals            |

## Create and Configure

<Steps>
  <Step title="Choose the field type">
    In the current table, click add field and choose **Link**.
  </Step>

  <Step title="Choose the target table">
    In the configuration dialog, choose the table to link to, such as linking the orders table to the customers table.
  </Step>

  <Step title="Choose the link mode">
    Choose a one-way or two-way link as needed.
  </Step>

  <Step title="Configure relationship rules">
    Use **Allow multiple selection** and **Allow duplicate values** to configure one-to-one, one-to-many, many-to-one, or many-to-many relationships.
  </Step>
</Steps>

## One-Way and Two-Way Links

| Mode         | Description                                                                                                                                  | Best for                                                                                                  |
| ------------ | -------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------- |
| Two-way link | Enabled by default. When you create a link field, Teable creates a corresponding link field in the target table, and both sides stay in sync | Relationships that need to be viewed from both tables, such as orders and customers or projects and tasks |
| One-way link | When the two-way option is off, only the current table shows the linked records. The target table does not get a reverse field               | Cases where you only need to reference another table and do not want to change the target table structure |

## Relationship Types

Use **Allow multiple selection** and **Allow duplicate values** together to define four common relationship types:

| Relationship           | Business example                                                                                                  | Configuration                                                                                   |
| :--------------------- | :---------------------------------------------------------------------------------------------------------------- | :---------------------------------------------------------------------------------------------- |
| **One-to-one (1:1)**   | **Employee - Profile**<br />One employee has one profile, and one profile belongs to one employee                 | ☐ Allow multiple selection<br />☐ Allow duplicate values<br />*(both options off)*              |
| **One-to-many (1:N)**  | **Department - Employee**<br />One department has multiple employees, but each employee belongs to one department | ☑ Allow multiple selection<br />☐ Allow duplicate values<br />*(only allow multiple selection)* |
| **Many-to-one (N:1)**  | **Task - Project**<br />Multiple tasks belong to one project, but each task belongs to only one project           | ☐ Allow multiple selection<br />☑ Allow duplicate values<br />*(only allow duplicate values)*   |
| **Many-to-many (N:N)** | **Student - Course**<br />One student can take multiple courses, and one course can have multiple students        | ☑ Allow multiple selection<br />☑ Allow duplicate values<br />*(both options on)*               |

## Common Uses

* **CRM customer management**: In a `Companies` table, create a link field to a `Contacts` table so one company can link to multiple contacts.
* **Project task assignment**: In a `Tasks` table, create a link field to a `Projects` table so each task belongs to one project, while the project table can show related tasks.
* **Order line items**: In an `Orders` table, link to a `Products` table, then use lookup fields to show prices and rollup fields to calculate order totals.

## Notes

* **One-to-many limits**: In a strict one-to-many relationship, when multiple selection is off on the Table B side, a Table B record linked by one Table A record cannot be selected by other Table A records. This works for data that should not be reused, such as ID numbers or employee profiles.

<Info>Link fields can only connect tables in the same Space. Lookup, Rollup, Conditional Lookup, and Conditional Rollup fields also need same-Space source data.</Info>