# Database Diagrams in SSMS

SSMS draws a database's tables and the foreign keys between them. Make a diagram of Northwind, read its keys and relationship lines, and know when to draw one.

Journeyman · Database · SQL · Updated November 3, 2026

## After this lesson you can

- Create a database diagram in SSMS and read its tables, keys and relationships

## Key takeaways

- In SSMS, right-click Database Diagrams under a database and choose New Database Diagram to see its tables and foreign keys.
- A key symbol beside a column marks the primary key, and each line between two tables is a foreign key relationship.
- The key end of a line is the one side and the ∞ end is the many side, so `Customers` to `Orders` reads one customer, many orders.
- Saving a diagram you've edited changes the database, so build from scripts and use a diagram to sketch and check your design.

A script lists the tables one after another. A **diagram** shows them side by side, with lines for the foreign keys between them, so you can see how a database fits together at a glance.

## Making a diagram

1. In SSMS's **Object Explorer**, open **Databases**, then **Northwind**.
2. Right-click **Database Diagrams** and choose **New Database Diagram**.
3. The first time, SSMS asks to create the objects it needs to store diagrams. Click **Yes**.
4. In **Add Table**, select the tables you want (hold **Ctrl** to pick several, or select them all), click **Add**, then **Close**.
5. SSMS lays out the tables. Drag them around until the lines are easy to follow.
6. Save it (**Ctrl+S**) with a name, such as `Northwind Overview`. It appears under **Database Diagrams**.

If **Database Diagrams** gives an error about the database's owner, you can still read the structure in **Object Explorer**: each table's **Keys** folder lists its primary and foreign keys.

## Reading a diagram

| You see | It means |
|---|---|
| A box | A table, with its columns listed |
| A key symbol beside a column | That column is (part of) the primary key |
| A line between two boxes | A foreign key relationship |
| A key at one end of the line | The **one** side: the table whose primary key is referred to |
| An infinity symbol (∞) at the other end | The **many** side: the table that holds the foreign key |

So the line from `Customers` (key end) to `Orders` (∞ end) reads: *one customer, many orders*. `OrderDetails` has two lines, one to `Orders` and one to `Products`: it's the associative table that makes orders and products many-to-many.

Hover over a line to see its foreign key's name, such as `FK_Orders_Customers`.

## Designing with a diagram

You can also design in a diagram: add a table, add columns, and drag from a primary key column onto another table's column to make a foreign key. Saving the diagram changes the database.

That's handy for sketching, but this course builds databases from **scripts**, which can be read, kept in Git and run again. A good habit: design with a diagram or on paper, then write the script, then make a diagram from the finished database to check it matches your design.

## When to draw one

- **Before you build:** sketch the tables and lines on paper or in a drawing tool, to check every subject has a table and every link has a key.
- **When you meet a new database:** a diagram of its tables is the fastest way to learn which joins you'll need.
- **When you explain a design:** a picture of the tables and lines says more than the script.

## Check yourself

1 question to try on the lesson page.

## So what

A diagram turns a list of tables into a map. Before writing a join across five tables, a look at the diagram shows you the path.

## Key terms

- [Entity-Relationship Diagram (ERD)](https://www.ask-codey.com/glossary/entity-relationship-diagram-erd)
- [Cardinality](https://www.ask-codey.com/glossary/cardinality)

## Cheat sheets

- [Database Diagrams in SSMS](https://www.ask-codey.com/cheat-sheets/foundations-of-database-design-database-diagrams-in-ssms-cheat-sheet)

Source: https://www.ask-codey.com/lessons/foundations-of-database-design-database-diagrams-in-ssms