Career

SQL Interviews: What Companies Actually Test

SQL Mastery Team
April 27, 2026
5 min read

Welcome to **Phase 8: Career & Reality**! Today is **Day 96**, and we're talking about getting hired.

The Interview Myth

Many people think SQL interviews are about knowing every obscure command. They aren't. Companies want to see how you solve problems.

The "Top 3" Interview Topics

1. **Joins**: You *must* explain the difference between LEFT and INNER joins perfectly.

2. **Aggregations**: You'll be asked to calculate revenue per month or users per country. (Phase 2 & 18).

3. **The Window Trick**: "How do you find the 2nd highest salary?" (Phase 5).

The Strategy: Think Out Loud

The interviewer doesn't just want the code; they want to hear your logic:

  • "First, I'll join these tables on the user ID..."
  • "Then, I'll group them to get the total..."
  • "I'll use a LEFT JOIN to make sure we don't lose users without orders..."

    • Pro Tip: Ask About the Data

    Before you write a single line, ask: "Can this column be NULL?" or "Is this ID unique?" This shows you are a senior-level thinker who knows that real-world data is messy.

    Your Task for Today

    Practice explaining the difference between `GROUP BY` and `PARTITION BY` to a friend (or yourself in the mirror).

    *Day 97: Surviving a 'Database Down' Crisis.*

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