# ER diagram

> See a database's tables, columns, keys and the foreign keys between them as an entity-relationship diagram.

Source: https://fleetdock.dev/docs/er-diagram


A database's **Diagram** page draws its entity-relationship diagram (ERD): every table and view
with its columns, and a line for every foreign key between them. Fleetdock reads it from the
database itself, so it is always the current structure, whichever tool created it.

Open it with **Diagram** on the database page, or the diagram button above the table list in the
data browser. The page uses the whole window: the arrow at the top left goes back to the
database, and the full-screen button there also hides the browser's own toolbars.

## Reading the diagram [#reading-the-diagram]

* Each card is a table, or a view with a dashed border. The header shows its name (on
  PostgreSQL with the schema) and the engine's row estimate.
* Columns are listed in order with their type. A key icon marks the primary key, a link icon
  a column used by a foreign key, and `?` a column that accepts `NULL`. Very wide tables list
  their first 24 columns plus every key column, and say how many more there are.
* An arrow runs from the referencing column to the column it references: from
  `orders.customer_id` to `customers.id`. A **dashed** line is an optional relation, where
  every referencing column accepts `NULL`.

Click a table to highlight its relations and the columns they join; everything else fades.
Double-click a table, or click its name, to open it in the [data browser](/docs/data-browser).

## Schemas [#schemas]

On PostgreSQL, the diagram draws the schemas you chose, with the same choice as the data browser's
table list. The schema menu in the toolbar changes it. A foreign key between a shown table and a
table of another schema still appears: that table is drawn as a dashed card with
**Show schema**, which adds its schema to the diagram.

## Large databases [#large-databases]

* **Find a table** centres the diagram on it.
* **Neighbours** shows one table and the tables 1, 2 or 3 relations away. A database with
  more than 150 tables opens this way, on its most connected table.
* Choose fewer schemas (above) to draw less.

Small databases are laid out left to right, referencing tables before the tables they
reference; larger ones are arranged around their most referenced tables. Drag cards where you
want them: positions are kept in your browser until you press **Re-layout**.

## Export [#export]

The download menu saves the diagram as **PNG** or **SVG**, the whole diagram at full size,
for documentation or a design review.

## Permissions and limits [#permissions-and-limits]

The diagram shows what your own data access can see, like the data browser: tables you
cannot read are not drawn, and neither are relations to them. Up to 5000 tables, 100000
columns and 20000 foreign keys are read; a larger database shows a notice that only part of
it is drawn.

The data comes from `GET /v1/databases/{id}/diagram`.