Joins and Tableau

Joining in tableau is pretty simple , though with some limitations. The first thing you need is a data source with multiple tables, either a connection to a database server, or an excel workbook with multiple tabs.

To join two tables you simply drag and drop tables onto the data manipulation pane, Tableau will try to create a link between the two tables, looking for fields with similar or identical names and perform a join on them.

The default for these kinds of joins is the inner join, but tableau also offers the ability to do a left join, right join, or outer join. However its worth noting here that right and outer joins are not available for excel.

The Join dialogue is where different sorts of joins can be specified as well as the keys that are used to perform the join. Here, the join has been performed on ID, a fairly simple form of join.

If we try to join a pair of tables and Tableau can’t find the common key, Tableau will leave it up to us to select the key, this is where knowing your data is important. Once the key is selected we simply click anywhere to close the dialogue box, and the join is set.

Joins in Tableau 9 and earlier can only be conducted between two tables from the same data sources, but from Tableau 10 onwards joins can be made between tables from different data sources, and no doubt this will open up a whole new realm for self service analytics. Watch this space for more on this in the coming months.

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