Unless you are applying for a team lead or management-focused role, preparing for data engineering interviews with 3.5 or 4 years of experience is no different from preparing for data engineering interviews with, say, 2 years of experience or less.

The interview process for data engineering roles, from my experience, seems to cover the following:

Coding exercises:

1. Programming challenges. These could be in either Python, Scala, or Java. The aim here is to grasp your understanding of basic data structures, such as lists and hash maps, and the use of basic loops and iterations. These challenges normally get progressively harder and involve debugging or adding new features to start a discussion with the interviewer. The best way is to practice examples on platforms like HackerRank.

2. SQL. The aim here is to understand how you would query different tables within a database and perform selects, joins, and aggregations to present and solve a business problem. Again, practicing examples with basic joins and the use of aggregate functions will help. You are almost guaranteed a question that will involve aggregating and grouping by certain columns.