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How do you convert 3 rows into one column in SQL?

SQLeasy0.2 min read

**STRING_AGG** (PostgreSQL): SELECT STRING_AGG(col, ', ' ORDER BY id) FROM (SELECT col FROM t LIMIT 3) sub. **LISTAGG** (Oracle), **GROUP_CONCAT** (MySQL), **ARRAY_AGG** (returns array). For exactly 3 rows: LIMIT 3 in subquery. **Determinism**: ORDER BY in agg....

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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
Globant
Key Concepts Tested
sql

Why This Question Matters

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

How to Approach This

Start by clearly defining the core concept being asked about. Interviewers want to see that you understand the fundamentals before diving into implementation details. Structure your answer with a definition, then explain the practical application with a concise example.

Expert Answer
44 words

STRING_AGG (PostgreSQL): SELECT STRING_AGG(col, ', ' ORDER BY id) FROM (SELECT col FROM t LIMIT 3) sub. LISTAGG (Oracle), GROUP_CONCAT (MySQL), ARRAY_AGG (returns array). For exactly 3 rows: LIMIT 3 in subquery. Determinism: ORDER BY in agg. Null handling: STRING_AGG ignores NULL by default.

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According to DataEngPrep.tech, this is one of the most frequently asked SQL interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

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