The CData Power BI Connector for Avalara supports standard SQL joins like the following examples.

Inner Join

An inner join selects only rows from both tables that match the join condition:

SELECT c.Date, o.ItemCode, o.IsItemTaxable, o.Description FROM Transactions c INNER JOIN TransactionLines o ON c.Id = o.TransactionId

Left Join

A left join selects all rows in the FROM table and only matching rows in the JOIN table:

SELECT c.ContactName, o.CustomerCode, o.Name, o.Value FROM Customers c LEFT JOIN CustomerCustomFields o ON c.CustomerCode = o.CustomerCode Where c.CompanyId = '247015' And o.CompanyId = '247015'