> For the complete documentation index, see [llms.txt](https://docs.tableplus.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tableplus.com/gui-tools/working-with-table/constraint.md).

# Constraint

## **NOT NULL Constraint**

You can specify a NOT NULL constraint on a column from the Table Structure view:

* Open the table structure view (**`⌘ + ^ + ]`**)
* Specify the value of the **`is_nullable`** field to:
  * **`YES`** to add NOT NULL constraint.
  * **`NO`** to remove the NOT NULL constraint.
* Press **`⌘ + S`** to commit changes to the server.

![](https://2743975646-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LriZ7WXXZykpg6_MQsw%2F-LsTPxWlqDE2ZyPYvgrx%2F-LsTTOqltm4z4bKIW91d%2Fnot-null.gif?alt=media\&token=8a4d8bf6-1b25-4299-aacf-c094b5d54a38)

## **PRIMARY KEY** Constraint

You can specify a Primary Key Constraint on a column from the Table Structure view:

* Open the table structure view (**`⌘ + ^ + ]`**)
* Specify the value in the Primary Key box:
  * Add the column name into the Primary Key box to make it a define the Primary Key Constraint on that column.
  * Delete the column name from the Primary Key box to remove the Primary Key Constraint on that column.
* Press **`⌘ + S`** to commit changes to the server.

![](https://2743975646-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LriZ7WXXZykpg6_MQsw%2F-LsTPxWlqDE2ZyPYvgrx%2F-LsTVZHK7ICUzSlnNt4f%2Fprimary-key.gif?alt=media\&token=147b0f48-b170-4437-b25b-5146f1d35646)

## FOREIGN KEY **constraint**

You can specify a Foreign Key Constraint on a column from the Table Structure view:

* Open the table structure view (**`⌘ + ^ + ]`**)
* Click on the **`foreign_key`** field and choose **`Create a foreign key on column`**
* From the popup, specify the foreign relationship.
* Press **`⌘ + S`** to commit changes to the server.

![](https://2743975646-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LriZ7WXXZykpg6_MQsw%2F-LsTPxWlqDE2ZyPYvgrx%2F-LsTWtkpXXLoL7kq7Arw%2Fforeign-key.png?alt=media\&token=c69100cd-0b17-465f-827c-acc2eb7379b6)

## DEFAULT Constraint

You can specify a default value for a column from the Table Structure view:

* Open the table structure view (**`⌘ + ^ + ]`**)
* Specify the default value in the **`column_default`** field. It's **`NULL`** by default.
* Press **`⌘ + S`** to commit changes to the server.