– 统计表中总数据量
select count(*) from student;

– 唯一索引查询：student_no列有唯一索引
select * from student where student_no = ‘2025021027’;

– 普通索引查询：student_name列有普通索引
select * from student where student_name = ‘学生_21035’;

– 无索引查询：email列没有建立索引
select * from student where email = ‘student_21035@qq.com’;

– 主键索引查询：id列是主键（自带主键索引）
select * from student where id = 9527;