摘要： 组函数AVGCOUNTMAXMINSUMVARIANCE：方差STDDEV：标准差SELECT AVG(salary), MAX(salary),MIN(salary), SUM(salary)FROM employeesWHERE job_id LIKE '%REP%';SELECT MIN(hire_date), MAX(hire_date)FROM employees;COUNT(expr) 返回expr为非空值的行数:SELECT COUNT(commission_pct)FROM employeesWHERE department_id = 80;select cou 阅读全文