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MySQL GROUP BY

The GROUP BY clause is used to group rows that have the same values in specified columns. It is often used with aggregate functions such as COUNT, SUM, AVG, etc., to perform calculations on each group.

Examples with Tamil Kings

1. Grouping by Reign Period

SELECT reign_period, COUNT(*) AS king_count FROM tamil_kings_auto_increment
GROUP BY reign_period;

Code Explanation: This query groups records by reign_period and counts the number of kings in each group.

2. Using GROUP BY with Multiple Columns

SELECT reign_period, kingdom, COUNT(*) AS king_count FROM tamil_kings_auto_increment
GROUP BY reign_period, kingdom;

Code Explanation: This query groups records by both reign_period and kingdom, counting the number of kings in each combination of groups.

Best Practices

  • Use GROUP BY to aggregate data and derive meaningful insights from groups of records.
  • Ensure that all columns in the SELECT statement that are not aggregated are included in the GROUP BY clause.

Key Takeaways

  • The GROUP BY clause groups rows with the same values into summary rows.
  • It is often used with aggregate functions to summarize data.
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