Wednesday, 25 March 2015

What is the difference between joining and blending in Tableau? Tableau Interview Question

Tableau Interview Question:
What is the difference between joining and blending in Tableau?
Ans:-
Joins in Tableau: 
For EX: your client is in Healthcare domain and using SQL Server as their database. In SQL server there may be many Tableau like Claims Table, Rejected Claims Table, Customers Table.  Now, client wants to know customer wise Claims and customer wise rejected Claims. Here you have to make use Joins concept to combine the data from Join Customers table with Claims and Customer table with Rejected Claims table using the Joins. Join is a query that combines the data from 2 or more tables by making use of Join condition.
We can join max 32 table, it’s not possible to combine more than 32 tables.
In Tableau the joins can perform in 2 ways.
1. By making use of common columns.
2. By making use of common data types.

If we create joins on the fields in Tableau all the table names are suffixing with $.
While performing the joins on multiple tables, always go with the less amount of data tables, so that we can improve the performance.

In Tableau the joins are divided into 2 types.
1. Equi Join, 
2. Non Equi Join.

1. Equi Join: in the join condition if we are using Equality “=“operator then such a kind of join called as Equi Join.

2. Non Equi Join: in the join condition apart from the Equality “=“if we use any other operator like <, >, <=, >= and =! Then such a kind of joins are called as Non Equi Join

Equi Join is divided into 3 types.

1. Inner Join,
2. Outer Join,
3. Self-Join.

1. Inner Join: Inner join will loads the only matching records from the both tables.
Inner join condition: Tableaa.id = Tableb.id

2. Outer Join
Again the outer join divided into 3 types.
           a. Left Outer Join,
           b. Right Outer Join,
           c. Full Outer Join.

Left Outer Join: displays the complete data from the left + matching records from the right.
Condition: tablea.id = tableb.id (+).

Right Outer Join: displays the complete data from the right + matching records from the left.
Condition: tablea.id (+) = tableb.id

Full Outer Join: full outer join load the complete data from the left table and right table.
Condition: Table A full outer join Table B ON tablea.id = tableb.id

3. Self-Join: if we are performing join to the same table itself such a kind of join called as self-join.

Non Equi Join: 
In the join condition if we are using the operators apart from the equality “=” then such a kind of joins are called as non equi join.


Data Blending in Tableau: 
For Ex: Your client is same Healthcare Client. They are operating their services in Asia, Europe, NA and so on & the are maintaining Asia data in SQL, Europe Data in SQL Server and NA data in MY SQL.
Now, your client wants to analyze their business across the world in a single worksheet. So you cant perform join here..
Now you have make use of Data Blending Concept.
Normally in the Tableau we can perform the analysis on the single data server. If we want to perform the analysis from the multiple data sources in a single sheet then we have to make use of a new concept called as data blending.
Data blending mix the data from the different data sources and allow the users to perform the analysis in a single sheet. Blending means mixing. If we are mixing the data sources then it is called as data blending.
Rules to perform the data blending
In order to perform data blending there are few rules.
1. If we are performing the data blending on 2 data source these 2 data sources should have at least 1 common dimension.
2. In that common dimension at least 1 value should match.

In Tableau we can perform the data blending in 2 ways. 
1. Automatic way
2. Custom way
1. Automatic way: 
in the automatic way Tableau automatically defines the relationship between the 2 data sources based on the common dimensions and based on the matching values and the relationship is indicated with Orange color.
2. Custom or Manual way: 
in the manual or custom way the user need to define the relationship manually .

Data blending functionality
1. While performing the data blending each work sheet has a primary connection and optionally it might contains several secondary connections.
2. All the primary connections are indicated in the Blue in the work sheet and all the secondary data sources indicated with the Orange color tick mark.
3. All the primary data sources and the secondary data sources are linked by specific relationship.
4. In the data blending 1 sheet contains 1 primary data source and 1 sheet can contain end number of secondary data sources.

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