Query in MySQL

One 、 Create index

create table student(
  sid int primary key,
  card_id varchar(20), 
  name varchar(20),
	gender varchar(20), 
	age int,
	birth date,
  phone_num varchar(20), 
	score double,
  index index_name(name) --  to name Column creation index 
);
select * from student where name =' Zhang San ';

2. Create directly ：

create index index_gender on student(gender);

3. Modify table structure to add index

alter table student add index index_age(age);

– Look at the index ：