[单项选择]A nation’s merchant marine is made up of its commercial ships and people ()them. A. they operate B. who operate C. they operate of D. do they operate
第21题: [单项选择]有SQL语句: SELECT主讲课程,COUNT(*)FROM教师GROUP BY主讲课程 该语句执行结果含有的记录个数是 A. 3 B. 4 C. 5 D. 6 参考答案:D 答案解析:[解析]使用COUNT()函数以及分组GROUP BY构造查询,该SQL语句的结果有多少条记录可以根据GROUP BY后面的字段进行判断,该语句以主讲课程字段为分组依据,可以查看原数据表,发现主讲课程