The grouping command in mysql is

MySQL's group command is used to group records by a specified column or expression and summarize values ​​within the same group. The most common grouping command is GROUP BY, which divides records into groups by a specified column or expression and applies an aggregate function to each group to summarize and calculate values. MySQL also supports nested GROUP BY and other grouping commands such as ROLLUP, CUBE, and GROUPING SETS for more complex grouping operations.

Group command in MySQL

The group command in MySQL is mainly used to group the records in the query results according to Groups by a specified column or expression, summarizing and aggregating values ​​within the same group. The most common grouping command is GROUP BY.

GROUP BY syntax

<code class="sql">SELECT 分组列, 聚合函数(列)
FROM 表名
WHERE 条件
GROUP BY 分组列</code>

Where:

• Group column: One or more specified grouping basis column or expression.
• Aggregation function: Function used to summarize and calculate values ​​within the same group, such as SUM(), COUNT(), AVG(), etc.
• Column: The column or expression to be aggregated.

Usage

GROUP BY command divides the records in the query results into multiple groups, each group contains the same grouping All records of column values. It then applies an aggregation function to the values ​​in each group, producing an aggregated result.

For example, the following query uses GROUP BY to group customers by country and count the number of customers in each country:

<code class="sql">SELECT country, COUNT(*) AS customer_count
FROM customers
GROUP BY country;</code>

NESTED GROUP BY

MySQL allows the use of nested GROUP BY to group data on multiple levels. For example, the following query groups customers by country and city and counts the number of customers from each country in each city:

<code class="sql">SELECT country, city, COUNT(*) AS customer_count
FROM customers
GROUP BY country, city;</code>

Other grouping commands

except# In addition to ##GROUP BY, MySQL also provides other grouping commands, including:

• ROLLUP: used to create multi-level groups and summarize values ​​at each level.
• CUBE: Used to create multidimensional groups and summarize all possible combinations of dimensions.
• GROUPING SETS: Allows grouping by multiple group sets.

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