Joins vs Blend vs CrossDatabase Join

Joins

Joining is a method of combining data based on the common fields.
The result of combining data using join is a table that is extended horizontally by adding columns of data.
Join combines data at the data source level.
In joining firstly the record wise matching is performed and then the data aggregates.
There are four types of joins:-

Inner join
Left outer join
Right outer join
Full outer join

☛ Inner join- The result of Inner join is a table that contains values that have common members from both the tables.

☛Left outer join- The result of Left outer join is a table that contains common members from both the tables and also all values from the left table.

☛Right outer join- The result of Right outer join is a table that contains common members from both the tables and also all values from the right table.

☛Full outer join- The result of Full outer join is a table that contains all values from both the tables.

Joins are used when there are multiple tables from the same data source to be used in the dashboard.
If the rows do not match then the resulting table contains null values.

Blending

Data blending is also a method of combining data from multiple sources.
Blending brings in additional information from the secondary data source and displays it with data from the primary data source which is already in the view.
Blends query each data source independently.
Blending occurs at visualization level.
In blending first aggregation occurs and then record wise matching is seen.
Blending is used when the data sources have a different level of granularity.
The blend is a smart join.
It automatically creates a left outer join.
Blending is preferred when there are multiple tables from different data sources to be used in the dashboard.
The new data source can be added by going to Data>New Data Source.
The primary data source is indicated by a blue checkmark on the data source and secondary data source is indicated by an orange checkmark.
While blending, if the user sees an orange linking field icon in front of a field in the data pane, it means the data source is automatically linked. As long as there is at least one active link, the data can be blended.
If the user sees a grey broken link icon in front of a field in the data pane, it means the data source is not linked, click on the icon to activate blending.
When blending is applied if there are multiple matching values for each mark in the primary data source, then the resultant table will contain asterisks.

Cross database joins

Cross database join is a new feature in Tableau.
In this type of join, the data is crossed between different sources.
The data in crossed much faster and without any additional technical knowledge.
The two databases can be a combination of a CSV file and excel file, MySQL and excel file etc…
It allows the user to cross data between different data sources in a much easier way and intuitive manner.
The primary data source is indicated by a blue checkmark on the data source and secondary data source is indicated by an orange checkmark.
When blending is applied user can see asterisks for multiple matching values but in cross database join asterisks are not seen.
This is a very interesting improvement that many Tableau users needed.
Cross database joins cannot be used with some connection types, some of them are listed below.