Press the expression or function groups:
Case #: The number of employees grouped according to the length of the employee's name, query the number of employees in each group were screened greater than five
SELECT
COUNT(*),LENGTH(last_name)
FROM
employees
GROUP BY
LENGTH(last_name)
HAVING
COUNT(*)>5;
By grouping multiple fields:
# Example: query the average wage of employees in each department in each trade
SELECT
AVG(salary),department_id,job_id
FROM
employees
GROUP BY
department_id,job_id;
Sort
# Case: query each department department number each trade is not null employees average salary> 10000, and the display according to the level of the average wage
SELECT
AVG(salary),department_id,job_id
FROM
employees
WHERE
department_id IS NOT NULL
GROUP BY
department_id,job_id
HAVING
AVG(salary)>10000
ORDER BY
AVG(salary) DESC;