MySQL groupby

MySQL的GROUP BY语句可以将查询结果按照一个或多个列进行分组，并对每个分组进行聚合操作，例如计算每个分组中的总数、平均值等。GROUP BY语句的基本语法为：
SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
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其中，column_name(s)表示要进行分组的列名，可以是一列或多列，多列之间用逗号隔开。condition表示查询条件。在GROUP BY语句中，SELECT子句中的列名必须是分组列或聚合函数（如SUM、AVG、MAX、MIN等）。
例如，下面的示例查询每个部门的员工数和平均工资：
SELECT department, COUNT(*) AS total_count, AVG(salary) AS avg_salary
FROM employees
GROUP BY department;
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该语句将employees表按照department列进行分组，统计每个部门的员工数和平均工资，并将结果返回。

相关问题

mysql group by avg_mysql~group by

GROUP BY is a clause in MySQL that is used to group rows that have the same values in a specific column or columns.
AVG is a function in MySQL that is used to calculate the average of a set of values.
So, if you want to group rows by a specific column and then calculate the average for each group, you can use both GROUP BY and AVG together.
For example, let's say you have a table called "sales" with columns "region" and "sales_amount". You can use the following query to group the sales by region and calculate the average sales amount for each region:
SELECT region, AVG(sales_amount) FROM sales GROUP BY region;
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This will return a result set that shows each region and its average sales amount.

mysql group by distinct

distinct和group by在MySQL中用于进行数据分组的操作。在MySQL 8.0之前，group by会进行隐式排序，可能导致性能下降，而distinct则没有这个问题。但是从MySQL 8.0开始，MySQL删除了隐式排序，所以在语义相同且无索引的情况下，group by和distinct的执行效率几乎是相同的。此外，group by和distinct都可以使用索引，它们的效率也是相同的，因为distinct可以被看作是特殊的group by。