mysql 分组函数的特性

发布时间：2023-07-31 15:08:22 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

#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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