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A SQL query is slow. How do you diagnose and optimize it?

Query tuning is a core data-engineering skill, and the signal is reading the execution plan before changing anything, then applying the right fix. Here is the diagnostic method that separates guessers from engineers.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.

Query tuning is a core data-engineering skill, and the signal is reading the execution plan before changing anything, then applying the right fix. Here is the diagnostic method that separates guessers from engineers.

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