How to Design ERD Diagrams and Export SQL DDL in Schema Editor

TLDR

Open Schema Editor in ERD Mode, click to place entity tables, and declare columns with their data types and Primary Key (PK) or Foreign Key (FK) constraints. Drag relationship lines between tables to set standard Crow's Foot cardinality (1:1, 1:N, N:M), then click Export SQL DDL to generate clean, production-ready CREATE TABLE migration scripts for PostgreSQL, MySQL, or SQLite.

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Before you start

You need a relational database model in mind (such as an e-commerce schema with users, orders, and products) and a web browser.

Schema Editor compiles visual entity graphs into SQL DDL scripts locally in your browser with zero server latency or data leakage.

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Step 1 — Switch to Software / ERD Mode

In the top mode selector of Schema Editor, choose ERD Mode (or navigate to /tools/schema-editor/software/).

The left toolbar populates with entity design tools: Table Entity, Crow's Foot Connector, Note Card, and Schema Group Box.

Step 2 — Create entity tables and declare columns

Click Add Entity Table in the left toolbar (or press E).

1. Click on the canvas to place a new table node.
2. Double-click the header to name your table (e.g. users).
3. Click Add Column to create attribute rows for id, email, created_at, etc.

Repeat this step to create a second table named orders with columns id, user_id, and total_amount.

Step 3 — Set Primary Keys, data types, and unique constraints

Select an entity table to view its column configuration panel on the right:

• Data Types: Choose standard SQL types (UUID, VARCHAR(255), BIGINT, TIMESTAMP, BOOLEAN, NUMERIC(10,2)).
• Primary Key (PK): Click the key icon on id to flag it as the table's primary key.
• Nullability & Uniqueness: Toggle NOT NULL or UNIQUE on required attributes like email.

Step 4 — Connect tables with Crow's Foot relationships

Click the Connector Tool (C or the relationship icon in the toolbar).

1. Click and drag from the users table to the orders table.
2. A relationship line snaps between the two entities.
3. In the right-hand Cardinality settings, select One-to-Many (1:N).
4. The connector updates its line endings with standard Crow's Foot notation: a single cross-stroke on the users side and a three-prong crow's foot on the orders side.

Step 5 — Configure Foreign Key cascade rules

Select the relationship line to inspect its foreign key properties:

• Source Column: users.id
• Target Column: orders.user_id
• On Delete Action: Choose CASCADE, SET NULL, or RESTRICT.

The visual line labels update to reflect the constraint relationship.

Step 6 — Export executable SQL DDL or Mermaid syntax

Click Export in the top action bar:

• SQL DDL (.sql): Generates formatted, executable CREATE TABLE and ALTER TABLE ... ADD CONSTRAINT scripts. Choose your SQL dialect (PostgreSQL, MySQL, SQLite, or CockroachDB).
• Mermaid ER (.mmd): Copies Mermaid ER diagram markup for embedding directly into GitHub READMEs and markdown documentation.
• Vector SVG (.svg): Exports clean vector graphics for architecture review slides.

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Pro tip: multi-dialect SQL target selection

Different SQL databases handle auto-incrementing IDs and timestamps differently (e.g. PostgreSQL SERIAL / UUID vs MySQL AUTO_INCREMENT).

When exporting SQL DDL, click the dialect dropdown in the export dialog to generate dialect-accurate syntax (such as PostgreSQL UUID PRIMARY KEY DEFAULT gen_random_uuid() or SQLite INTEGER PRIMARY KEY AUTOINCREMENT).

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Next steps

• Design sequence diagrams with Mermaid export
• Model state machines with XState v5 export
• Convert unstructured text into SQL tables in Table Formatter