查询平均成绩良好， 也就是≥80 分的考生人数， 查询语句就可以写成____。 A: SELECT COUNT(*) FROM (SELECT eeid,avg(achieve) FROM eeexam GROUP BY eeid) AS avgach (eeid,avgachieve)WHERE avgachieve>=80; B: SELECT COUNT(*)FROM (SELECT eeid,avg(achieve)FROM eeexamGROUP BY eeid) avgach (eeid,avgachieve)WHERE avgachieve>=80; C: SELECT dname,(SELECT COUNT(*)FROM examinerWHERE department.dname = examiner.erdepa)FROM departmentWHERE avgachieve>=80; D: SELECT *FROM erexam NATURAL LEFT OUTER JOIN exampaper;

查询选修了数学课(课程号为2)的学生人数,可以使用的查询语句是:　 。 A: SELECT MAX(*) FROM SC WHERE Cno = 2; B: SELECT AVG(Sno) FROM SC WHERE Cno = 2; C: SELECT COUNT(*) FROM SC WHERE Cno = 2; D: SELECT COUNT(Sname) FROM SC WHERE Cno = 2;

通过 SQL，您如何返回 "Persons" 表中记录的数目？ A: SELECT COLUMNS() FROM Persons B: SELECT COLUMNS(*) FROM Persons C: SELECT COUNT() FROM Persons D: SELECT COUNT(*) FROM Persons

查询选修了课程的学生人数，SQL语句为SELECT COUNT(DISTINCT S#) FROM SC

智慧职教: select count(*) from student as s1语句主要查询s1表中的数据个数。