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Top 10 most important interview questions for Tableau developer 2021

1.     What are the different types of filters in Tableau?
Tableau filters are used to restrict the data flowing through tableau workbooks, worksheets and dashboards, etc.
There are different types of filters in tableau are as follow:
a.      Data source Filter
b.      Context filter
c.      Extract Filter
d.      Dimension Filter
e.      Measure Filter
f. Quick Filters

2. What are LOD expressions and explain LOD? 

 Level Of Detail expressions are used to check the granularity of the data and allows to compute the values at different levels of detail. If you want the data at more granular level then INCLUDE LOD will be used or if you want the data at exact level then FIXED LOD will be used or if you want the data at lesser granular level then EXCLUDE LOD can be used.

 So there are 3 types of LODs:

3. How to optimize the performance of the Tableau dashboard?

There are multiple ways to optimize the performance of tableau dashboards:
1. Remove unused columns or fields in data source.
2. Use extract filters for data sources
3. Use context filters if applicable
4. Use boolean and integer data types rather than using String data type. Computer process boolean and integer data types faster than Strings.
5. Use Min/Max aggregation instead of Average as processing time for average is slower as compared to Min/Max.
6. Remove marks from your sheets.
7. Use continuous data filters.
8. Reduce the use of nested calculations in your visuals.
9. Remove custom SQLs wherever possible. 

4. What are Sets, groups, and what are the differences?

Sets: Tableau sets are conditional groups created by grouping different dimensions and measures.
Groups: Tableau groups are simply grouping of lower level dimensions to create higher level category.

Difference between Sets and groups:

Sets are created by using conditions while groups don’t require any condition to create it. 

Sets are dynamic in nature while Groups are not dynamic.

If we have created a set of Top 5 customers by profit and a group of top 5 customers by profit, then when after some time the profit changes then group values will be as it was and the values of set will be changing and it will show the correct results.

One more difference: We can not use group in calculation while set can be used.

5.What is the difference between a heat map and a tree map?

                                                    Tree map Vs Heat map

Tree Map 

Heat Map

Data is represented
as nested rectangles, colors and size of rectangles.

Data is represented by
the different color codes.

It is used for
comparing the categories with colors, size, and it can also be used for
illustrating the hierarchical data and part to whole relationships.

It is used for
comparing the categories based on color and size. And also, it is great in
spotting the patterns based on the density of the information.

Colors and size of
rectangles are respective to the data points 

When their values
are higher or density of records, the data will represent in dark color.

6. List all the file extensions in Tableau.

 The below ones are few extensions in Tableau:

  1. Tableau Workbook (.twb)
  2. Tableau Data extract (.tde)
  3. Tableau Datasource (.tds)
  4. Tableau Packaged Datasource (.tdsx)
  5. Tableau Bookmark (.tbm)
  6. Tableau Map Source (.tms)
  7. Tableau Packaged Workbook (.twbx) – zip file containing .twb and external files.
  8. Tableau Preferences (.tps)


7. How to create the top 5 and bottom 5 customers in a single sheet?
If you want to show the top 5 and bottom 5 customers in the same view then follow below steps:

1. Create a set of top 5 customers.
2. Again create a set of bottom 5 customers.
3. Now, press Ctrl and select both the sets and right click on it. Select create combined set.
4. Name it ‘top and bottom customers’ and include all members of both sets.
5. Now add this field into the filter shelf. Check your view of Customers by profit contains only top 5 and bottom 5 customers.


8. What is a parameter in Tableau and how it differs from filters?

Parameters are dynamic values used to replace the constant values in calculations.
Parameters are like variables which we can used in tableau calculations. That is parameters allows only single value. 
So that parameters have single select options in UI except checkboxes, which have multiple selection and not single value selection.

While filters are simple and straightforward to use to restrict the data. It can be applied on dimension and measures directly.

For example, to show the revenue generated by states Maharashtra and Gujrat in country India, we will directly apply filter on States dimension. So that revenue for only Maharashtra and Gujrat will be available in view and we can change the UI options to see the filter like Checkbox, radio button, drop-down, etc.

9. Explain Row Level Security in Tableau.

Row Level Security (RLS) is the process of restricting the data from specific users and allow access to certain users to specific workbooks.

10. Difference between Extract and Live database connection in Tableau.

 Extract database is the snapshot of the data, which is offline data source where we can analyze the data without database connection. Or whatever we will do is irrespective of database connection. When you create extract data Tableau does not require access to database for visual analytics and processing is faster.
Live database is the real time database where whatever we will do in data source will be reflected in tableau. So Live data is directly connected and affects the visuals. If larger data volume will results into performance issues.

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