How to Join tables in Tableau?

[vishrut-singhal]

Tableau Data Joining

Data joining is a common requirement in any data analysis. You may need to join data from different tables in a single source or join data from multiple sources.

Tableau provides the feature to join the tables by using the data pane that is available in the Data menu.

A join means combining columns from one or more tables in a relational database. It also creates a set that can be saved as a table, or it can be used as it is.

Joins are specifies into five types:

1. Cross Join.
2. Inner Join.
3. Natural Join.
4. Outer Join.
5. Left Outer Join.
6. Right Outer Join.
7. Full Outer Join.
8. Self-Join.

Overview of Types of Joins

A join section is used to combine rows from two or more tables, based on a related column between them.

1. Cross Join: Cross join produces rows which combine each row from the first table with each row from the second table.

2. Inner Join: An inner join returns the matching rows from the tables that are being joined.

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3. Natural Join: Natural join is not used any comparison operator. It does not concatenate the way.

Only we can perform a Natural Join if there is at least one common attribute that exists between two relations. Also, the attributes must have the same name and domain .

Natural join works on those matching attributes where the values of attributes in both the relation are same.

4. Outer Join: An outer join is an extended form of the inner join.

It returns both matching and non-matching rows for the tables that are being joined.

Types of outer joins are as follows:

i) Left Outer Join: The left outer join returns matching rows from the tables being joined, and also non-matching rows from the left table in the result and places NULL values in the attributes that come from the right table.

ii. Right Outer Join: The right outer join operation returns matching rows from the tables being joined, and also non-matching rows from the right table in the result and places NULL values in the attributes that come from the left table.

iii. Full Outer Join: The full outer join is used to combine tables. As a result, it contains all values from both tables.

When a value from a table doesn’t have a match with the other table, then it returns a NULL value in the data grid.

5. Self-Join: The self-join is used to join a table with itself. It means that each row of the table is combined with itself as well as with every other row of the table.

Creating a Join in Tableau

Let’s assume a data source Sample-superstore to create a join between two tables such as Orders and Returns .

• Go to the Data menu and choose Microsoft Excel option below connect .
• Then select sample-superstore as a data source and click the Open button.
• Drag Orders and Returns tables from sheets of the data source to the data pane . After that Tableau will automatically create a join between Orders and Returns tables which can be changed later as per required joins.

• Below screenshot shows the building inner join between Orders and Returns tables by using the Order id field.

Edit a Join Type in Tableau

Tableau automatically creates a type of join between two tables, but it can be changed as per need.

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• Click on the middle of two circles that showing the auto-created join.
• After clicking, a popup window appears which shows all the four types of the joins.
• In below screenshot, you can see all the joins such as inner join , left outer join , right outer join , and full outer join .

How to Edit Join Fields in Tableau

• Also, you can change the fields by clicking the Data Sources option to add a new join clause that is available in the join popup window.
• While selecting the field, you can search for the field using a search text box.