GROUP BY is used to group and summarize the data in the table by specified columns, and use aggregate functions (such as SUM, COUNT, AVG) to make statistics on the data in the group. The syntax is SELECT aggregate_function(column_name) AS alias FROM table_name GROUP BY column_name.
GROUP BY clause: Grouping data in MySQL
What is GROUP BY?
The GROUP BY clause is used to group data in a table according to specified columns. After grouping, it performs aggregate functions such as SUM, COUNT, AVG, etc. on each group to summarize and count the data within the group.
Syntax:
<code class="sql">SELECT aggregate_function(column_name) AS alias FROM table_name GROUP BY column_name</code>
Parameters:
Working principle:
The GROUP BY clause works through the following steps:Example:
The following example uses the GROUP BY clause to find the number of employees in each department:<code class="sql">SELECT department_id, COUNT(*) AS num_employees FROM employees GROUP BY department_id;</code>
Note:
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