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mysqlsqlgroup-by

what are aggregated columns in mysql?

What are aggregated columns and non-aggregated columns? I have read the MySQL Handling of GROUP BY and am confused. I do not know what 'aggregated columns' mean. Does anybody know?

MySQL Handling of GROUP BY link

Solution

  • Functions like SUM, AVG, MAX, MIN, COUNT calculate data over a group of records and return aggregated results.

    E.g.

    SELECT SUM(`salary`) FROM `employees`;

    Returns 1 row with the total salary when

    SELECT `salary` FROM `employees`;

    Returns multiple rows with the salary per employee.

    Lets say you want the average salary per gender:

    SELECT `gender`, AVG(`salary`) FROM `employees` GROUP BY `gender`;

    Query 1 & 3 contain aggregated columns: SUM(`salary`) AND AVG(`salary`)