Question 1

What is an ER diagram?

Accepted Answer

An ER (Entity-Relationship) diagram is a visual representation of a database structure. It shows entities (tables), their attributes (columns), and relationships between them using crow's foot notation. ER diagrams are essential for planning database schemas before implementation.

Question 2

Can I import SQL to create an ER diagram?

Accepted Answer

Yes! Click the 'Import SQL' button in the toolbar to paste your CREATE TABLE statements. The tool automatically detects PostgreSQL, MySQL, SQLite, and SQL Server syntax, extracts tables, columns, primary keys, foreign keys, and unique constraints, and generates a Mermaid ER diagram with proper relationships and cardinality.

Question 3

What do the crow's foot symbols mean?

Accepted Answer

Crow's foot notation uses symbols at the ends of relationship lines: || means 'exactly one' (mandatory), o| means 'zero or one' (optional), |{ means 'one or more', and o{ means 'zero or more'. For example, CUSTOMER ||--o{ ORDER means one customer can have zero or more orders.

Question 4

What is the difference between identifying and non-identifying relationships?

Accepted Answer

Identifying relationships (solid lines with --) mean the child entity cannot exist without the parent — the foreign key is part of the child's primary key. Non-identifying relationships (dashed lines with ..) mean the child can exist independently. For example, an ORDER_ITEM identifies through ORDER, but a PRODUCT has a non-identifying link to CATEGORY.

Question 5

What is the difference between an ER diagram and a database schema?

Accepted Answer

An ER diagram is a conceptual model showing entities and relationships visually. A database schema is the actual implementation — the SQL tables, columns, and constraints. ER diagrams help you plan; schemas are what you build. You can go from schema to diagram using our SQL import feature.

Question 6

How do I show primary and foreign keys?

Accepted Answer

Add PK, FK, or UK after the attribute name. You can combine markers: 'uuid id PK' for a primary key, 'uuid user_id FK' for a foreign key, 'string email UK' for a unique constraint. Multiple markers can be comma-separated: 'uuid id PK,FK'.

Question 7

Which SQL dialects are supported for import?

Accepted Answer

The SQL import feature supports PostgreSQL, MySQL, SQLite, and SQL Server (T-SQL). It auto-detects the dialect from keywords like SERIAL (PostgreSQL), AUTO_INCREMENT (MySQL), or IDENTITY (SQL Server). You can also manually select the dialect.

Question 8

Is this ER diagram tool free?

Accepted Answer

Yes, completely free including the SQL import feature. Design your database schema visually, import SQL DDL, define entities with attributes and relationships, and export as PNG, SVG, or PDF. Sign in to save diagrams to the cloud for free.

Element	Syntax	Description
Entity	`ENTITY { }`	Define a database table
Attribute	`type name`	Column with data type
Primary Key	`type name PK`	Primary key column
Foreign Key	`type name FK`	Foreign key referencing another entity
Unique Key	`type name UK`	Column with unique constraint
Comment	`type name PK "comment"`	Add a description to any attribute
Exactly one	`\|\|`	Exactly one (mandatory)
Zero or one	`o\|`	Optional (zero or one)
One or more	`\|{`	At least one (mandatory many)
Zero or more	`o{`	Optional many
Identifying	`A \|\|--o{ B : label`	Solid line — strong dependency
Non-identifying	`A \|\|..o{ B : label`	Dashed line — weak dependency

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