索引到底有什么用,听说能提高查询效率?
select id,uname,passwd from user;
如果我在uname字段建立了普通索引,那么经过怎样的查询后就能提高速度;
请好好讲讲!
迷茫2017-04-17 14:39:54
Indexes are generally used in where or table association conditions to improve query efficiency. If you simply select username from user, it will scan the entire table.