mysql จากโค๊ด sql นี้ ถ้าเราจะทำ between ต้องใช้ยังไงเหรอครับ

$sql="SELECT  project_name_thai,project_name_eng,ref_project_year,year_id,project_year  ";
$sql.=" FROM project RIGHT JOIN year ON project.project_year=year.year_id ";
 $sql.="WHERE (project_name_thai like '%".$_GET['txtKeyword']."%' or project_name_eng like '%".$_GET['txtKeyword']."%')  AND  (year.year_id ='$year1'  or project.project_year='$year1'  ) OR (year.year_id ='$year2'  or project.project_year='$year2' )  ";