删除表student中班级（CID）为 6的全部学生信息，下面SQL语句正确的是：D A delete * from student where cid = 6; B delete * from student on cid = 6; C delete from student on cid = 6; D delete from student where cid = 6; PG中，下面可以加速全文搜索的索引有哪些？AD A gist B btree C hash D gin 在PostgresSQL中,枚举类型的值大小写是否敏感？B A 否 B 是 PostgresSQL的时间类型可以精确到秒以下。A A.正确 B.错误