额,看错了,正确的应该写法是
${if(len(studentno) == 0,"","and studentno in ('" + studentno+ "')")}
SELECT * FROM STSCORE WHERE COURSE = 'English'
${if(len(classNo) == 0,"","and CLASSNO IN('" + classNo+ "')")}
${if(len(studentNo) == 0,"","and STUDENTNO in ('" + studentNo+ "')")}