The role of groupby in sql

SQL GROUP BY clause organizes a data set by grouping and aggregating data by columns. It is used to: Group tables by specified columns Apply aggregate functions (such as SUM, AVG, COUNT) to calculate group values

GROUP BY sub-sub in SQL Sentence

The GROUP BY clause is a powerful tool in SQL that allows users to group data sets by one or more columns and aggregate data for each group.

Function

The main functions of the GROUP BY clause are as follows:

• Group the data set according to the specified column
• Aggregate data for each group, such as calculating sums, averages, or counts

Syntax

The syntax of the GROUP BY clause is as follows:

<code>SELECT 列名1, 列名2, ...
FROM 表名
GROUP BY 列名3, 列名4, ...</code>

• Column name 1, column name 2, ...: the column to be selected
• table name: the table to be queried
• column name 3, column name 4, . ..: The column to be grouped

Usage example

The following is an example of using the GROUP BY clause:

<code>SELECT department, SUM(salary)
FROM employees
GROUP BY department</code>

This query Group the employees table by the department column and calculate the total salary for each department.

Aggregation Functions

The GROUP BY clause is often used with aggregate functions that calculate values ​​for each group. Some common aggregate functions include:

• SUM(): Calculate the sum
• AVG(): Calculate the average
• COUNT(): Calculate the count
• MIN(): Calculate the minimum value
• MAX(): Calculate the maximum value

Multiple column grouping

GROUP BY sub Sentences can be grouped by multiple columns at the same time. For example:

<code>SELECT department, location, SUM(salary)
FROM employees
GROUP BY department, location</code>

This query groups the employees table by the department and location columns and calculates the total salary for each department and location.

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