mysql 分组函数的特点

发布时间：2023-05-06 12:50:40 所属栏目：MySql教程来源：

导读：#能排序就能比较,并且忽略了null值
SELECT MAX(last_name),MIN(last_name),COUNT(last_name) FROM employees;
#count只能计算不为null的个数
SELECT COUNT(commission_pct) FROM employees;
#忽略了null值
SELE

#能排序就能比较,并且忽略了null值
SELECT MAX(last_name),MIN(last_name),COUNT(last_name) FROM employees;
#count只能计算不为null的个数
SELECT COUNT(commission_pct) FROM employees;
#忽略了null值
SELECT SUM(commission_pct),AVG(commission_pct) FROM employees;
#与去重连用
SELECT SUM(disTINCT salary),SUM(salary) FROM employees;#distinct去重
SELECT COUNT(disTINCT salary) ,COUNT(salary) FROM employees;

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