What does group by mean in sql

GROUP BY is an aggregate function in SQL, used to group data based on specified columns and perform aggregation operations. It allows users to: Group data rows based on specific column values. Apply an aggregate function (such as sum, count, average) to each group. Create meaningful summaries from large data sets, perform data aggregation and grouping.

GROUP BY in SQL

GROUP BY is an important aggregate function in SQL, which allows users to Specify columns to group the data, and then perform an aggregation operation (such as SUM, COUNT, AVG, etc.) on each group.

How to use GROUP BY?

The GROUP BY clause is used in the SELECT statement, and its basic syntax is as follows:

<code>SELECT 聚合函数(列名)
FROM 表名
GROUP BY 列名</code>

For example, to pair Employee## based on the Department column # To group the data in the table and calculate the total number of employees in each department, you can use the following query:

<code>SELECT COUNT(employee_id)
FROM employees
GROUP BY department_id</code>

How GROUP BY works

GROUP BY will convert the data Rows in the table are grouped based on specified column values. It combines rows with the same grouping column value to form a group. It then applies the specified aggregate function to each group, producing an aggregated result.

Advantages of GROUP BY

• Data summaries: GROUP BY can be used to quickly create meaningful summaries from large data sets.
• Data aggregation: It allows users to perform various aggregation operations on grouped data, such as calculating sums, averages, or counts.
• Data Grouping: GROUP BY can be used to divide data into different categories or groups to facilitate analysis and visualization.

The above is the detailed content of What does group by mean in sql. For more information, please follow other related articles on the PHP Chinese website!