For most relational data sources you can connect to a specific query rather then the entire data source. Often this can be useful when you know exactly the information you need and you understand how to write SQL queries.
- Select Custom SQL in the connection dialog box.
- Type or paste the query into the text box. The button in the upper right corner of the text box opens a larger editing window for more complex queries.
When you finish the connection, only the relevant fields display in the Tableau Data window.
If your SQL query references duplicate columns, you may get errors when trying to use one of the columns in Tableau. This will happen even if the query is valid. For example, consider the following query:SELECT * from authors, titleauthor where authors.au_id = titleauthor.au_id
The query is valid, but the au_id field is ambiguous because it exists in both the “authors” table and the “titleauthor” table. Tableau will connect to the query but you will get an error anytime you try to use the au_id field. That’s because Tableau doesn’t know which table you are referring to.