Lesson 16 of 20

Check NULL, duplicates and consistency

Turn quality intuition into measurable, repeatable SQL controls.

33 minSQL Essentials

By the end of this lesson

  • Measuring a completeness rate
  • Detect duplicates
  • Reconcile two totals

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Check NULL, duplicates and consistency is part of the complete programme: 20 lessons, 44 verifiable exercises and 2 published guided projects.

  • Complete content with explained examples
  • SQL simulator and expected result
  • Detailed answer, common mistakes and challenge
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