How to use the concat function in mysql

//Query the year and month of the managefee_managefee table, and use the concat function to form year-month. For example, 2017 and 1 are combined to form 2017-01. .
select CONCAT(a.year,'-',if(a.month<=9,CONCAT('0',a.month),a.month))as date,a.* from managefee_managefee as a;

//Query the data in managefee_managefee with the time period from 2017-01 to 2017-07 select * from
(
select CONCAT(a.year,'-',if(a.month<=9,CONCAT('0',a.month),a.month))as date,a.* from managefee_managefee as a
) b
where b.date between '2017-01' and '2017-07';