The CData Power BI Connector for Microsoft Excel Online 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.Name, o.ItemCount, o.TotalCost, o.Date FROM Spreadsheet1_Customers c INNER JOIN Spreadsheet1_Orders o ON c.Id = o.CustomerId

Left Join

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

 SELECT c.Name, o.ItemCount, o.TotalCost, o.Date FROM Spreadsheet1_Customers c LEFT JOIN Spreadsheet1_Orders o ON c.Id = o.CustomerId