Free skill reference · Data & analytics

SQL JOINs — combine tables step by step

Learn INNER JOIN and LEFT JOIN with a tiny practice dataset. Useful for analysts, ops, and anyone who reports from spreadsheets.

  1. Identify the shared key between two tables.
  2. Start with INNER JOIN to keep matching rows only.
  3. Switch to LEFT JOIN when you need all rows from the left table.
  4. Check counts before and after the join to catch duplicates.

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