【单选题】学生选课信息表SC(sno,cno,grade),主码(sno,cno),从学生选课信息表中找出无成绩的元组的SQL语句是( )
A.
Select * from SC where grade=null
B.
Select * from SC where grade IS ‘’
C.
Select * from SC where grade=’’
D.
Select * from SC where grade is null
【单选题】设SC表中记录成绩的列为:Grade,类型为int。若在查询成绩时,希望将成绩按‘优’、‘良’、‘中’、‘及格’和‘不及格’形式显示,正确的 Case表达式是( )。
A.
Case Grade When 90~100 THEN ' 优' When 80~89 THEN ' 良' When 70~79 THEN ' 中' When 60~69 THEN ' 及格' Else ' 不及格' 1.End
B.
Case When Grade between 90 and 100 THEN Grade = ' 优' When Grade between 80 and 89 THEN Grade = ' 良' When Grade between 70 and 79 THEN Grade = ' 中' When Grade between 60 and 69 THEN Grade = ' 及格' Else Grade = ' 不及格' 1.End
C.
Case When Grade between 90 and 100 THEN ' 优' When Grade between 80 and 89 THEN ' 良' When Grade between 70 and 79 THEN ' 中' When Grade between 60 and 69 THEN ' 及格' Else ' 不及格' End
D.
Case Grade When 90~100 THEN Grade = ' 优' When 80~89 THEN Grade = ' 良' When 70~79 THEN Grade = ' 中' When 60~69 THEN Grade = ' 及格' Else Grade = ' 不及格' End
【单选题】切口平移法脱氧核苷酸探针标记方法,使用的酶为()
【简答题】grade是成绩信息表,curriculum是课程信息表,建立一个视图v_cavg,该视图包括了课程编号和(该课程的)平均成绩两个字段,正确的SQL语句是( )。A. Credate View v_cavgAS课程编号,AVG(分数)AS 平均成绩From grade Group by 课程编号 B. Credate View v_cavgASSELECT课程编号,AVG...
【单选题】学生选课信息表SC(sno,cno,grade),主码为(sno,cno),从学生选课信息表中找出无成绩的元组的SQL语句是( )。
A.
SELECT * FROM sc WHERE grade=NULL
B.
SELECT * FROM sc WHERE grade IS ‘‘
C.
SELECT * FROM sc WHERE grade=‘‘
D.
SELECT * FROM sc WHERE grade is NULL
【单选题】切口平移法脱氧核苷酸探针标记方法,使用的酶为
【单选题】对于学生信息表:student(sno,sname,sex,age,grade),查询学习成绩为空的学生的学号和姓名,下面语句正确的是
A.
SELECT sno,sname FROM student WHERE grade=NULL
B.
SELECT sno,sname FROM student WHERE grade IS NULL
C.
SELECT sno,age FROM student WHERE grade IS NULL
D.
SELECT sno,age FROM student WHERE grade=NULL
【单选题】用缺口平移法标记DNA探针时,常用()。