MySQL創建和刪除索引
創建普通索引：
alter table student add index index_dept(dept(8));
創建唯一索引
create unique index uni_ind_name on student (name);
根據列的前n個字符創建索引
create index index_dept on student(dept(8));
根據多個列創建聯合索引
create index ind_name_dept on student(name,dept);
根據多個列的前n個字符創建聯合索引
create index ind_name_dept on student (name(8), dept(10));
刪除普通索引
alter table student drop index index_dept;
drop index index_dept on student;