There are many ways to create data connections in tableau. It is important that these connections are made correctly so that our visuals stay relevant and insightful. Avoiding leading our audience down a wrong path. In the coming text, ways to create connections between data are explored.

 

Joins

Joins are used when you would like to combine rows from one or more tables. They are joined on a common field that is present in one table, that is also the primary key in at least one table.

To access joins in tableau, first you’ll need to make sure you’ve uploaded your desired dataset. Drag on the desired table onto the data source  pane, and it’ll bring up the logical table. This will be where we make our relationships later. Double-click on the table to bring up the physical table. Here we are able to bring on the other table we would like to join by. Now we can specify which fields we would like to join on, as well as the type of join we’d like to create. Once you’ve got that configured, the tables will have successfully been joined.

 

Unions

Unions are used when you would like the add rows from two tables on top of each other. These tables need to have common fields for the union to work. For example, say you have a table from sales in the first quarter and sales in the second quarter. Using a union, you can add those sales tables into one table that contains sales from quarter 1 and 2.

To do this in tableau, once again move to the data source tab. Once here, add the table you would like to exist at the top on the union. There are many ways to make unions. One way is to simply drag the second table just underneath the first until the union icon appears. The other way is to drag a union onto the data source pane, and add the tables you’d like to union manually.

 

Once you’ve specified all the tables you’d like to union, the result will be a new table containing all the rows in common fields.

 

Relationships

Relationships are much like joins, in that you have to relate them using common fields, however, where they differ is that relationships keep tables separate. The tables in a relationship are not joined together to combine or add rows, simply a relationship is made between the tables.

In order to make a relationship, once again navigate to the data source tab and drag a table onto the pane in which you’d like to make relationships with. Staying on the logical tables, drag another table onto the pane next to the first table so that a connection is made between them. On this connection line, you’ll be able to define how you would like to relate these two tables together using common fields.

 

Once you’ve defined this relationship, you can continue to add more tables to create more relationships, or you can move on and start visualising.

data connections

Blends

When creating data blends, the data sources will remain separate. One data source will become the primary source (the one you use first on that sheet), whilst the other will become secondary, utilising aggregated measures to create links between data sources.

To make a blend, the process is pretty simple. Make sure you’re connected to both the data sources you’d like to utilise first. Then choose a dimension or measure from the data source you’d like to make the primary data source. Now whenever you use a field from the secondary source, it will appear as an aggregated measure. It’s important to note that you will not be able to sort by any field from the secondary source. So be careful with choosing your primary and secondary sources.

 

Understanding the different types of connections can be confronting at first. However, after some time utilising the different connections, it will definitely become more natural.

 

References:

By John Lyu, a data school graduate who describes within this blog what a primary key is:

Data Modeling 101: A Beginner’s Guide to Success

By Tara de Gelder, another great description on tableau data connections:

https://theinformationlab.nl/en/2023/08/04/understanding-relationships-joins-unions-and-blends-in-tableau-combining-data-sources/