What does the group by statement in sql mean?

The GROUP BY statement is used to group data by specified columns or column combinations, and perform aggregate functions (such as sum, count, average) on each group to summarize the data. The syntax is: SELECT column 1, column 2, ...FROM table name GROUP BY grouping column

GROUP BY statement in SQL

The GROUP BY statement is used to group data and aggregate records in the same group together. By dividing data into different groups, it helps us summarize information, identify patterns, and simplify results.

Syntax

<code>SELECT 列1, 列2, ...
FROM 表名
GROUP BY 分组列</code>

Where:

• Column 1, Column 2,. .. is the column to be retrieved.
• Table name is the table to be grouped.
• Group column is the column or combination of columns to be used for grouping.

Function

The GROUP BY statement groups data based on the value of the grouping column, and then performs an aggregate function (such as SUM(), COUNT(), AVG()) to summarize the data.

Example

Consider a table containing student scores:

<code>| 学号 | 学生姓名 | 数学成绩 | 语文成绩 |
|---|---|---|---|
| 1 | 李华 | 90 | 85 |
| 2 | 王强 | 85 | 90 |
| 3 | 李明 | 95 | 80 |
| 4 | 张伟 | 80 | 95 |</code>

If we want to group by student name and calculate the average math score for each student , you can use the following GROUP BY statement:

<code>SELECT 学生姓名, AVG(数学成绩) AS 平均数学成绩
FROM 学生成绩表
GROUP BY 学生姓名</code>

The result will be:

<code>| 学生姓名 | 平均数学成绩 |
|---|---|
| 李华 | 87.5 |
| 王强 | 85.0 |
| 李明 | 87.5 |
| 张伟 | 82.5 |</code>

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