group by having
时间: 2023-08-25 10:07:53 浏览: 49
"GROUP BY" and "HAVING" are clauses used in SQL to perform aggregate functions on data.
"GROUP BY" is used to group the result set based on one or more columns. It is used with aggregate functions like COUNT, SUM, AVG, MIN, and MAX to calculate the result for each group.
For example:
```
SELECT department, COUNT(*) AS num_employees
FROM employees
GROUP BY department;
```
This query will group the employees by department and count the number of employees in each department.
"HAVING" is used to filter the result set based on the result of an aggregate function. It is similar to the "WHERE" clause, but the "WHERE" clause filters individual rows while the "HAVING" clause filters groups.
For example:
```
SELECT department, AVG(salary) AS avg_salary
FROM employees
GROUP BY department
HAVING AVG(salary) > 50000;
```
This query will group the employees by department and calculate the average salary for each department. The "HAVING" clause will filter out any departments with an average salary less than or equal to 50000.
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