GROUP BY

What is GROUP BY

• GROUP BY groups rows that have the same column value into one group.
• Each group then produces exactly one row in the result table.
• It is always used together with aggregate functions like SUM, AVG, COUNT, MIN and MAX.
• Grouping happens after the WHERE clause has filtered the rows.

Rules of GROUP BY

• Every column in the SELECT list that is not inside an aggregate function must appear in the GROUP BY clause.
• NULL values form their own single group.
• The result order is not guaranteed. Add ORDER BY if sorted output is needed.
• Example:-
  -- Total salary per domain SELECT Domain, SUM(Sal) FROM Employee GROUP BY Domain; -- Number of employees in each grade, sorted by grade SELECT Grade, COUNT(*) FROM Employee GROUP BY Grade ORDER BY Grade;