Looker Interview Questions

1) Explain about BI

Ans: Organizations small and large, carry out several processes or transactions which will result in generating humongous data. The data holds valuable information that could help improve business. That’s where the Business Intelligence tools come into the picture and help us explore data in meaningful ways. Processing the data in time and proper reporting enhances the ability to make more informed and data-driven decisions.

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2) What is SSIS?

Ans: SSIS is the abbreviation for SQL Server Integration Service. It is a component of the Microsoft SQL Server database and is used to build workflows for data migration tasks. It is an ETL tool that extracts data from different sources, transforms it, and loads it in a different destination.

3) Explain the categories of data flow?

Ans: There are three categories in the data flow.

• Sources - The sources can be excel files, flat files, XML files, Relational databases, etc.
  Transformations - Filter data based on some calculations, changing the format of the data, etc.
  Destinations - The destinations can be excel files, flat files, PDF files, XML files, relational databases, etc.

4) What do you mean by Looker BI?

Ans: Looker's business intelligence software helps in exploring and analyzing data. We can combine data from different sources and create a unified view. We can then build real-time analytics on top of the data and share them easily. It offers great visualizations and drill-down dashboards.

5) What are the advantages of Looker BI?

Ans: Here are some of the many advantages of Looker BI.

• It generates a base model so we can work on the relationships 
• All the employees in an organization can have a centralized view of metrics
• We can create easy to read dashboards that allow users to find patterns 
• It connects directly to the database instead of loading the data from it
• We can share the generated reports across the organization

6) Explain about OLTP

Ans: Online transaction processing (OLTP) supports data processing of transaction-oriented applications. It focuses on the day to day transactions of an organization. It involves updating, inserting, deleting small chunks of data in a database. Since it operates on data of small size, the processing speed is faster.

7) Which one among File System Deployment and the SQL server deployment better?

Ans: The SQL Server Deployment is preferred when compared to File System Deployment. The processing time is faster, so it gives quick results. It also won't compromise the safety of the data.

8) What are the cache modes available?

Ans: There are three modes available in Looker.

• Full cache mode - All the values will be cached.
• Partial cache mode - Only the distinct values will be cached.
• No-cache mode - No data will be cached.

9) Explain about full cache mode

Ans: Full cache mode is the default cache mode selection. The reference result set will be cached before the execution. It will then retrieve and store the entire set of data from the specified lookup location. Full cache mode is best used when we have to deal with a large data set.

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10) Give the differences between no-cache mode and partial cache mode

Ans: The no-cache mode is used when the reference data set is very large to load into memory. The partial cache mode is used when the size of the data is relatively small. The lookup index in the partial cache mode is well-indexed and gives faster responses.

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11) Do logs have a relation with the packages?

Ans: Yes, the logs are related to the package level. You can enable logging for the package through the logging configuration.

12) Give the differences between DTS and SSIS

Ans: The following are some of the differences between DTS and SSIS.

• Data Transformation Services (DTS) is the predecessor of SSIS.
• DTS can extract, transform, and load data to or from a database. The SSIS tool can work with different sources and destinations.
• DTS has a limited set of transformations when compared to SSIS.
• DTS does not support BI tools integration. SSIS supports the end to end process of BI.
• DTS uses Activex Script, and SSIS uses VB.NET.

13) Define drill-down analysis

Ans: Drill down is a capability provided by most BI tools. It helps in viewing the data in a detailed manner and gives in-depth insights. You can drill-down on a component in a report or dashboard to get more granular details of it.

14) What is the use of the

Ans: The "Rebuild Derived Tables and Run" button is used to rebuild all persistent derived tables given in the query. It will also rebuild all the upstream PDTs.

15) How can we reference a derived table within the SQL of another derived table?

Ans: Yes, we can reference a derived table within the SQL of another derived table by using a concept called cascading. You can use the following syntax to achieve it.

${.}

16) Does Looker require access to the scratch schema to write ephemeral derived tables?

Ans: No, we don't have to set up a scratch schema. For the MySQL family of databases, we need to perform some additional setup to allow ephemeral derived tables.

17) What are Native Derived Tables (NDTs)?

Ans: The Native derived tables (NDTs) is defined in the LookML. We can create a native derived table by specifying the explore parameter on the base table with desired columns.

18) Define pivoting

Ans: Looking at data in multiple dimensions makes it easy to consume the data visually. To change the dimensions, we can use the pivot option that turns a dimension into a column. We can only change the pivoted dimensions order by changing the sort order.

19) Explain user flow analysis by heap in Looker

Ans: Heap captures user behavior like clicks, taps, gestures, and more across websites and applications automatically. It allows data enrichment with custom APIs. This will help in analyzing user actions and present them visually.

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20) What are the important steps of an analytics project?

Ans: Below are the important stages of an analytical project.

• Data exploration
• Data definition.
• Data modeling
• Data validation
• Data preparation

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21) Tell me some common troubleshooting steps for PDTs

Ans: The high-level steps of troubleshooting PDTs are,

• Check the state of the PDT
• Check the state of the regenerator
• Check the permissions and locking

22) Can we use templated filters in PDTs?

Ans: Using templated filters is not usually recommended. The table will be rebuilt every time the filter changes, and it causes a lot of strain on the database.

23) Why are copies of tables created in the same PDT of a database?

Ans: When you change the SQL of a derived table and query it, a new copy of the table is built in the PDT. The table copies only get created when the SQL in dev mode is different from the production mode. 

24) Does the sort order matter when using an offset list function?

Ans: The sort order is very important when using an offset list function. It defines whether to go up the table or down the table. 

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25) Can we base a table calculation on a particular pivoted column?

Ans: Yes, we can base a table calculation on a particular pivoted column using the pivot_where function. The column given for the pivot_where field specifies that it should be targeted for calculation.

26) What are the requirements for using custom visualizations?

Ans: Enable the Sandboxed Custom Visualizations Labs Feature in the admin panel. Install the custom JavaScript visualizations in the Visualizations page. Also, ensure that you have the latest version of the Chromium renderer.

27) Can we filter data using table calculations?

Ans: Yes, we can filter data using yes or no logic in table calculations.

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28) What data is included in table calculations?

Ans: Table calculations run after the query has returned. They operate on the data in the explore table.

29) What are the Looker blocks?

Ans: Looker Blocks are the pre-built pieces of LookML code that accelerate analytics. We can use these Looker blocks and customize them to your specifications. They enable building quick and flexible analytics.

30) Name the types of Looker blocks