针对上面的salaries表emp_no字段创建索引idx_emp_no

CREATE TABLE `salaries` (
`emp_no` int(11) NOT NULL,
`salary` int(11) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL,
PRIMARY KEY (`emp_no`,`from_date`));
create index idx_emp_no on salaries(emp_no);

select * from salaries indexed by idx_emp_no where emp_no = 10005;

select * from salaries force index(idx_emp_no) where emp_no = 10005