What does group by mean in sql

The GROUP BY clause is used to group data and perform aggregation operations based on groups. It groups groups of rows with the same value together and calculates summary values ​​or filtered data within each group.

GROUP BY: Data grouping

In SQL, the GROUP BY clause is used to group data so that Perform aggregation operations based on groups. Simply put, it groups together a set of rows with the same value.

Usage

The GROUP BY clause follows the SELECT clause and specifies the column or expression for grouping. For example:

<code>SELECT SUM(salary)
FROM employee
GROUP BY department;</code>

The above query groups the salary column in the employees table into the department column. Salaries for each department will be summed separately.

Benefits

GROUP BY provides the following benefits:

• Aggregation of data: For example, through SUM(), Aggregation functions such as COUNT() and AVG() are used to calculate summaries within groups.
• Filter data: Filter specific groups through the HAVING clause. For example, select only departments with a total salary greater than 10,000.
• Eliminate duplicates: Grouping can eliminate duplicate rows with the same value.

Note

• The GROUP BY column must appear in the SELECT clause, or an aggregate function must be used in the HAVING clause.
• If you do not specify a GROUP BY column, the entire table will be grouped, resulting in a single group.

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