一个表student中,有id,name,class...等字段,请问下如下语句的效率,及如何优化,2和3的区别:
1、select * from student where id='';
2、select * from student where name='';
3、select * from student where name='' and class ='';
1、select * from student where id='';
2、select * from student where name='';
3、select * from student where name='' and class ='';
create index x1 on student (id);2、select * from student where name='';
3、select * from student where name='' and class ='';
create index x2 on student (name,class);
1、select * from student where id='';
2、select * from student where name='';
3、select * from student where name='' and class ='';
id和name分别加索引
2和3的区别不是3多了一个过滤条件吗
create index x2 on student(name);
create index x3 on student(id,name);
create index x2 on student(name);
create index x3 on student(class,name);
这个没影响的!