Can you describe a situation where you had to solve a complex problem using your technical knowledge and skills?

The interviewer is asking this question to assess your problem-solving skills, technical knowledge, and how effectively you apply them in real-world situations. Break your answer down into the following three parts for a well-rounded response:

1. The context or description of the problem.
2. The steps you took to tackle the problem, and why you adopted such a strategy. Here, highlight your technical skill set.
3. The successful result, indicating that your problem-solving process was effective.

When I worked for XYZ Corporation as a Database Administrator, we had a serious issue where a significant number of records were misplaced due to a faulty data migration process. The significance of the issue was such that it could destabilize our application and it needed a quick fix without much downtime.

I decided to tackle it head-on. Leveraging my SQL knowledge, I began investigating the problem. I started by checking the data inconsistency between the source and destination databases.

I employed complex SQL queries, grouping and joining multiple tables, subqueries, and using various string and date functions. Additionally, I evaluated large volumes of data using SQL functionalities like limit, offset, etc.

This procedure was quite complex and also time-consuming given the large data volume, but the process worked and aided in identifying the data discrepancy patterns. I rectified the problem by writing scripts to correct the misplaced records. The result was a successful data correction with limited down-time and minimum disruption to our application.

At my previous job in ABC Company, our application had a performance issue where certain pages were loading slower than expected and resulted in a poor user experience. The problem was traced back to the database where the queries were taking longer to execute.

I used my technical SQL skills to optimize those queries that were contributing to the issue. I analyzed the queries using EXPLAIN PLAN and identified issues like full-table scans, missing indexes, and inefficient joins. Once the problems were pinpointed, I started refining the queries by creating necessary indexes and rewriting the joins where needed.

One particular complex situation I encountered was a query that included multiple joins and sub-selects. I rewrote the query using WITH clauses, resulting in a more efficient recursive query as opposed to sub-selects.

These corrective measures significantly improved page load times and enhanced the overall user experience. I was praised by the management team for my comfortable handling of this complex issue and the effective use of my SQL knowledge to address it.