To link multiple database tables in Crystal Reports, you can follow these steps :

1. Open Crystal Reports and create a new report or open an existing report.
2. Go to the "Database" menu and select "Database Expert." This will open the Database Expert window.
3. In the Database Expert window, you'll see a list of available data sources. Choose the appropriate data source or create a new connection to the database containing the tables you want to link.
4. Once you have selected the data source, you'll see the tables or views available in that database.
5. Select the first table you want to link and drag it to the "Links" tab.
6. Select the second table you want to link and drag it to the "Links" tab. Crystal Reports will automatically create a link between the two tables based on the common fields or keys. 7. If the link created by Crystal Reports is not accurate or if you need to customize the linking conditions, you can modify the link by clicking on the link line in the "Links" tab and selecting "Edit Link...".
8. In the "Edit Link" dialog box, you can specify the join type (e.g., inner join, left outer join, etc.) and customize the linking conditions by adding or modifying the join criteria.
9. If you need to link more tables, repeat steps 5 to 8 for each additional table, dragging them to the "Links" tab and adjusting the link conditions as needed.
10. Once you have linked all the desired tables, click "OK" to close the Database Expert window and return to the report design view.
11. You can now access fields from the linked tables and use them in your report design by dragging and dropping them onto the report canvas.