Senior ETL Tester Interview Questions and Answers

Inner join returns only the matching rows between two tables, while left join returns all rows from the left table and the matching rows from the right table.

• Inner join result: 1 2 3

• Left join result: 1 2 3, 4 5 6, 7 8 9

You can use a temporary table to change datatype without altering the original table.

• Create a new temporary table with the desired datatype

• Insert data from the original table into the temporary table

• Drop the original table

• Rename the temporary table to the original table name

Some tools used for ETL testing include Informatica PowerCenter, Talend, IBM InfoSphere DataStage, and Apache Nifi.

• Informatica PowerCenter

• Talend

• IBM InfoSphere DataStage

• Apache Nifi

To delete duplicates from a table, use a combination of SELECT DISTINCT and INSERT INTO new table.

• Create a new table with the same structure as the original table.

• Use SELECT DISTINCT to select unique rows from the original table.

• Insert the unique rows into the new table.

• Drop the original table.

• Rename the new table to the original table name.