1. Types of char

Type Size Range Extra Space Query Speed
CHAR Fixed 1~255 0 fast
VARCHAR Dynamic 1~65535 1~2 bytes slow
TEXT Dynamic 1~65535 2 bytes slowest

2. Index

Create index for database can speed up query.

2.1 How to create index

create index idx_name
on employee(name);
-- or
alter table employee
add index idx_name(name);

-- unique index
create unique index idx_name
on employee(name);

2.2 How to check index

show index from employee;

2.3 How to drop index

drop index idx_name
on employee;