Persistent Systems ETL Tester Interview Questions and Answers

Bug life cycle involves identification, reporting, fixing, retesting, and closing of software bugs.

• Identification of bug by tester

• Reporting bug with detailed information

• Developer fixes the bug

• Retesting to ensure bug is resolved

• Closing bug after verification

Entry criteria and exit criteria are conditions that must be met before and after testing, respectively.

• Entry criteria are the conditions that must be fulfilled before testing can begin

• Exit criteria are the conditions that must be fulfilled before testing can be considered complete

• Entry criteria can include having test data ready, test environment set up, and test cases prepared

• Exit criteria can include all test cases ...read more

Common validation techniques in ETL testing include data completeness, data accuracy, data transformation, and data quality checks.

• Data completeness validation ensures that all expected data is loaded into the target system.

• Data accuracy validation involves verifying that the data is correctly transformed and loaded without any errors.

• Data transformation validation checks if the data is transformed according to the bus...read more

Use SQL query with ORDER BY and LIMIT to fetch 5th highest salary.

• Use ORDER BY clause to sort salaries in descending order

• Use LIMIT 1 OFFSET 4 to fetch the 5th highest salary

Use SQL query to find the nth row and top 50% records using string function

• To find the nth row, use LIMIT and OFFSET in SQL query

• To find top 50% records, use PERCENTILE_CONT function in SQL

• String functions like SUBSTRING can be used to manipulate string data

Use SQL DATEDIFF function to calculate age from date of birth.

• Use DATEDIFF function to calculate the difference in years between current date and date of birth.

• Example: SELECT DATEDIFF(year, '2000-01-01', GETDATE()) AS Age;

• Make sure to handle leap years and edge cases like birthdate being in the future.

The SQL query to find records that never contain flag 0 in the critical column.

• Use the NOT EXISTS operator to check if there are no records with flag 0 for each distinct value in the critical column.

• Write a subquery to select distinct values from the critical column.

• Join the main table with the subquery using the critical column.

• Filter the result by checking if there are no records with flag 0 for each distinct value i

To validate between two integers, compare each corresponding digit and check if they are equal.

• Convert both integers to strings

• Pad the source integer with leading zeros to match the length of the target integer

• Compare each digit of the source and target integers

• If any digit is not equal, the validation fails

The question is asking to rearrange the numbers so that 100 is at the first row and the rest are below it.

• Create an array of strings to store the numbers

• Assign the value '100' to the first element of the array

• Use a loop to assign the numbers 1 to 99 to the remaining elements of the array

Set and join are operations used in database management systems.

• Set is used to perform mathematical set operations like union, intersection, and difference on two or more sets.

• Join is used to combine rows from two or more tables based on a related column between them.

• Set operations do not require a common column, while join operations do.

• Set operations return a result set with unique values, while join operations retur...read more

The output for inner join will be the rows where both col1 and col2 have non-null values.

• Inner join returns only the matching rows from both tables.

• In this case, the output will be the rows with non-null values in both col1 and col2.

• Rows with null or blank values in either col1 or col2 will be excluded from the output.

Slowly Changing Dimensions (SCD) are techniques used in data warehousing to track changes to dimension data over time.

• SCD Type 1: Overwrites old data with new data, losing historical information.

• SCD Type 2: Creates new records for each change, preserving historical data.

• SCD Type 3: Creates additional columns to track changes, allowing limited history.

• SCD Type 4: Uses separate tables to store historical and current data...read more

I worked on a data migration project for a retail company.

• Migrated data from legacy systems to a new ETL platform

• Ensured data integrity and accuracy during the migration process

• Created test cases and executed them to validate the data migration

• Collaborated with developers and business analysts to troubleshoot any issues

• Provided regular updates to stakeholders on the progress of the project