基本功能
DML
DDL
DCL
show语句
show engines
show databases;
show tables;
show status
show processlist
慢sql
索引
创建索引，删除索引的语法
alter table table_name add index index_name (column_list) ;
alter table table_name add unique (column_list) ;
alter table table_name add primary key (column_list) ;
create index index_name on table_name (column_list) ;
create unique index index_name on table_name (column_list) ;