1. show index 显示索引
show index from users
2. 添加key
alter table users add key key_name (name(4))
"key_name"是索引名字可以不写,默认是列名。
4是以前4个字符来索引,一定要写。
alter table users add key (name(4))
alter table users add primary key (indexcols...) alter table users add index [indexname] (indexcols...) alter table users add unique [indexname] (indexcols...) alter table users add fulltext [indexname] (indexcols...)
alter table users add foreign key [idxname] (column1) references table2 (column2) #外键
3. 删除key
alter table users drop key name
alter table users drop primary key alter table users drop index indexname alter table users drop foreign key indexname