For most databases, you’ll hook up with a selected query instead of the whole data set. Because databases have slightly different SQL syntax from one another , the custom SQL you employ to attach to at least one database could be different from the custom SQL you would possibly use to attach to a different . However, using custom SQL are often useful once you know precisely the information you would like and understand the way to write SQL queries.
Though there are several common reasons why you would possibly use custom SQL, you’ll use custom SQL to union your data across tables, recast fields to perform cross-database joins, restructure or reduce the dimensions of your data for analysis, etc.
For Excel and document data sources, this feature is out there only in workbooks that were created before Tableau Desktop 8.2 or when using Tableau Desktop on Windows with the legacy connection. to attach to Excel or text files using the legacy connection, hook up with the file, and within the Open panel , click the Open menu , then select Open with Legacy Connection.
Combine (join) and aggregate your data
If you would like to mix tables and aggregate your data, you’ll use both a join and default aggregation type options within the physical layer of the canvas in Tableau. In some cases you would possibly got to use custom SQL instead.