ER diagrams

PostgreSQL
MySQL
MariaDB

An ER diagram draws the tables of a database, or of one PostgreSQL schema, with their columns, keys and the relationships between them. Querybara reads the structure from the connection and lays the tables out for you. Use it to find your way around an unfamiliar schema, to see what a table is related to, or to export a picture for a document or review. To change the structure from the diagram, see ER model editing; to keep a model in a file, see Saved ER models.

The ER diagram of the shop schema with the orders table selected. Its related tables (customers, order_items, shipments) are highlighted with labelled 1:N and 1:1 relationships, and the rest are dimmed. The inspector lists orders' columns, its reference to customers and the order_items and shipments that reference it, including ON DELETE CASCADE. — Select a table to highlight its relationships and inspect its keys.

Open a diagram

Right-click an open connection, a database or a PostgreSQL schema in the sidebar (or use its Actions button) and choose ER diagram. The diagram opens in its own tab. On PostgreSQL, the Schema picker in the toolbar switches between All schemas and one schema.

If the database or schema has unapplied model changes from an earlier session, the diagram opens in edit mode with them; see Saved ER models.

Read the diagram

Each table is a box with its columns and their keys: P for primary key, F for foreign key, U for unique. Each foreign key is a line from the referencing column to the referenced column, with crow’s-foot ends:

The referenced end is “exactly one” when every referencing column is NOT NULL, and “zero or one” otherwise.
The referencing end is “zero or many”, or “zero or one” when its columns are the primary key or a unique key (one to one).

A foreign key that points outside the schema shown brings a stub of the referenced table, with only the referenced columns, drawn dashed. The canvas has a legend.

Arrange the diagram

Control	What it does
Columns shown: All, Keys, None	Every column, key and relationship columns only, or table names only
Types	Show or hide the column types
Views	Add the views (and materialized views) to the diagram
Auto layout	Arrange the tables automatically, related tables side by side
Fit	Fit the whole diagram in view
Edit model	Change the structure on the canvas (ER model editing)
Model	Open model file… and Save as model file… (Saved ER models)
Refresh	Read the structure again from the server
Tables	Show or hide the list of tables

Drag a box to move it. Your arrangement is kept when the diagram reloads, and tables that appear later are placed beside it. It lasts while the diagram tab is open; to keep it, save the diagram as a model file (Model → Save as model file…), which records where each box is.

Explore relationships

Click a table to select it. The diagram fades everything not related to it, and the details pane on the right shows its Columns, its References and what it is Referenced by. Each relationship there is a link to the other table. From the details you can also choose Open data, Design (the table designer), Only related and Hide.

Right-click a table on the canvas for Open data, Design table, Show only related tables, Hide from the diagram and Copy name.

Find, hide and show tables

Type in Find tables and columns (Ctrl + F, or Cmd + F on macOS) to filter the table list; matching boxes are ringed on the canvas. Esc clears the search, then the selection.
Click a table in the list to bring it into view.
Clear a table’s checkbox in the list to hide it. Show all brings every table back.
Only related (or Show only related tables) leaves the table and the tables it is related to.

Export

Choose Export in the toolbar.

Menu item	Result
SVG image…	A standalone SVG file
PNG image…	A PNG at twice the size
Mermaid diagram…	A `.mmd` file with a Mermaid `erDiagram`, for Markdown that renders it
As Mermaid	The Mermaid text on the clipboard
As SVG markup	The SVG on the clipboard

The export is drawn from the diagram itself, not captured from the screen. It uses light colours, includes the whole diagram whatever the zoom, and leaves hidden tables out.

The Mermaid text has an entity per table with its columns, types and keys, and a line per foreign key with the same crow’s-foot ends as the canvas. An excerpt:

erDiagram
    customers ||--o{ orders : "orders_customer_id_fkey"
    customers {
        integer id PK
        text name
    }

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