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Duplicate characters in a string (e.g., '123a!' to '112233aa!!').

SQLmedium0.3 min read

**Architectural Logic**: Character duplication is a string transform; SQL capabilities vary. **PostgreSQL**: `SELECT regexp_replace('123a!', '(.)', '\1\1', 'g')`. **Spark**: `regexp_replace(col("str"), "(.)", "$1$1")`. **Python**: `''.join(c*2 for c in s)`. **Why Choose**: SQL...

🤖 Analyze Your Answer
Frequency
Low
Asked at 1 company
Category
487
questions in SQL
Difficulty Split
130E|271M|86H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
HashedIn
Key Concepts Tested
joinpythonsparksql

Why This Question Matters

This medium-level SQL question appears frequently in data engineering interviews at companies like HashedIn. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (join, python, spark) will help you answer variations of this question confidently.

How to Approach This

Break this problem into components. Identify the core trade-offs involved, then walk the interviewer through your reasoning step by step. Demonstrate awareness of edge cases and production considerations - this is what separates good answers from great ones.

Expert Answer
64 words

Architectural Logic: Character duplication is a string transform; SQL capabilities vary. PostgreSQL: SELECT regexp_replace('123a!', '(.)', '\1\1', 'g'). Spark: regexp_replace(col("str"), "(.)", "$1$1"). Python: ''.join(c*2 for c in s). Why Choose: SQL regex works in many dialects; application layer clearer for complex manipulation. Scalability: For bulk, prefer batch processing in Spark/Python; SQL for inline transforms. Cost: UDF invocations in serverless add cost; native functions when possible.

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