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SQL · PRACTICAL GUIDE

SQL Conditional Aggregation

Build several KPI counts in one grouped query.

Practice SQLLearning path

What this solves

Count OK, missing and wrong scans per PO. This pattern is useful when the business question is clear but a generic tutorial is too abstract.

The rule

Put CASE expressions inside SUM or COUNT.

SELECT PO,
 SUM(CASE WHEN Status='OK' THEN 1 ELSE 0 END) OK_Count,
 SUM(CASE WHEN Status='MISSING' THEN 1 ELSE 0 END) Missing_Count
FROM Audit GROUP BY PO;

Real-work checklist

  1. Define the business key and expected grain before writing the formula, query or markup.
  2. Test the pattern on a small known sample where you can verify the answer manually.
  3. Check missing values, duplicates and data types before trusting a large result.
  4. Scale to the real file or database only after the logic is proven.

Common mistake

Use ELSE 0 so SUM returns predictable numeric results.

Try it next

PracticeChange the example and verify the result.Use a toolMove from a small example to real work.Related contentFind guides, errors and scenarios on this topic.