问答题select count（*） from student和select count（id） from student之间的区别是什么？

题目
问答题
select count（*） from student和select count（id） from student之间的区别是什么？
相似考题

1.统计每个部门中人数( )A.SELECT SUM(ID) FROM EMP GROUP BY DEPTNO;B.SELECT SUM(ID) FROM EMP ORDER BY DEPTNO;C.SELECT COUNT(ID) FROM EMP ORDER BY DEPTNO;D.SELECT COUNT(ID) FROM EMP GROUP BY DEPTNO;

2.对于学生信息表：student(sno，sname，sex，age，dept)，能够得到年龄在20岁到22岁之间的学生的姓名和学号的语句是A．SELECT * FROM student WHERE age BETWEEN 20 AND 22B．SELECT sname，sno FROM student WHERE age BETWEEN 20 AND 22C．SELECT sname，sno FROM student WHERE age＞=20D．SELECT sname，sno FROM student WHERE age＜=22

3.若student 表中有一字段s_fenshu，数据类型为整型，保存每个学生的考试成绩，求全班平均分的正确做法是：A.把每个学生的 s_fenshu 手工进行相加，然后除以全班人数，得到平均分B.使用 select avg(s_fenshu) from studentC.使用 select sum(s_fenshu) from student / select count(*) from studentD.使用 select sum(s_fenshu) from student % select count(*) from student

4.补全语句：select vend_id,count(*) from products where prod_price>=10 group by vend_id ____ count(*)>=2;

参考答案和解析
正确答案： select count（*）统计所有学生的记录个数，包括空记录。
select count（Id）统计所有学生的记录个数，不包括null记录。
解析： 暂无解析
更多“问答题select count（*） from student和select count（id） from student之间的区别是什么？”相关问题

  • 第1题：

    The STUDENT_GRADES table has these columns:STUDENT_ID NUMBER(12)SEMESTER_END DATEGPA NUMBER(4,3)The registrar requested a report listing the students‘ grade point averages (GPA) sorted from highest grade point average to lowest.Which statement produces a report that displays the student ID and GPA in the sorted order requested by the registrar? （）

    A. SELECT student_id, gpa FROM student_grades ORDER BY gpa ASC;

    B. SELECT student_id, gpa FROM student_grades SORT ORDER BY gpa ASC;

    C. SELECT student_id, gpa FROM student_grades SORT ORDER BY gpa;

    D. SELECT student_id, gpa FROM student_grades ORDER BY gpa;

    E. SELECT student_id, gpa FROM student_grades SORT ORDER BY gpa DESC;

    F. SELECT student_id, gpa FROM student_grades ORDER BY gpa DESC;


    参考答案：F

  • 第2题：

    根据SQL标准，查询表student(sno,sname,sex,dept)中所有学生的选修课程数，其中选修记录在表SC(sno,cno,grade)中，两表中sno为关联字段。下面哪条语句合适?()

    A select sno,count(cno) from SC

    B select sno,count(cno) from student

    C select a.sno,count(cno) from student a left outer join SC

    D select a.sno,count(cno) from SC left outer join student a


    参考答案C

  • 第3题：

    The STUDENT_GRADES table has these columns:The register has requested a report listing the students‘ grade point averages (GPA), sorted from highest grade point average to lowest within each semester, starting from the earliest date. Which statement accomplishes this?（）

    A. SELECT student_id, semester_end, gpa FROM student_grades ORDER BY semester_end DESC, gpa DESC;

    B. SELECT student_id, semester_end, gpa FROM student_grades ORDER BY semester_end ASC, gpa ASC;

    C. SELECT student_id, semester_end, gpa FROM student_grades ORDER BY semester_end, gpa DESC;

    D. SELECT student_id, semester_end, gpa FROM student_grades ORDER BY gpa DESC, semester_end DESC;

    E. SELECT student_id, semester_end, gpa FROM student_grades ORDER BY gpa DESC, semester_end ASC;


    参考答案：C

  • 第4题：

    已知有关系“STUDENT”，则关系运算σANE＜80(STUDENT)用SQL语句表示为(52)。

    A．SELECT( * )FROM STUDENT WHERE AVE ＜ 80

    B．SELECT( * )FROM STUDENT HAVING AVE ＜ 80

    C．SELECT(AVE)FROM STUDENT WHERE AVE ＜ 80

    D．SELECT(AVE） FROM STUDENT HAVING AVE ＜ 80


    正确答案：A
    解析：σAVE80(STUDENT)表示将关系STUDENT中满足条件“AVE80”的元组选择出来。

  • 第5题：

    select count（*） from student和select count（id） from student之间的区别是什么？


    正确答案: select count（*）统计所有学生的记录个数，包括空记录。
    select count（Id）统计所有学生的记录个数，不包括null记录。

  • 第6题：

    查询student表中的所有非空email信息，以下语句正确的是（）。

    • A、Select email from student where email !=null
    • B、Select email from student where email not is null
    • C、Select email from student where email <> null
    • D、Select email from student where email is not null

    正确答案:D

  • 第7题：

    下列查询语句中，错误的是（）。

    • A、SELECT Sno， COUNT（*） FROM SC GROUP BY Sno
    • B、SELECT Sno FROM SC GROUP BY Sno WHERE COUNT（*）> 3
    • C、SELECT Sno FROM SC GROUP BY Sno HAVING COUNT（*）> 3
    • D、SELECT Sno FROM SC GROUP BY Sno

    正确答案:B

  • 第8题：

    数据库中有一张表名称为Student，有列Number，Name，Age，IDCard，Sex。主键为Number。统计学生总人数，下列哪个SQL语句是正确的（）

    • A、Select Count（1）From Student
    • B、Select Sum（*）From Student
    • C、Selec tAvg（*）From Student
    • D、Select Count（*）From Student

    正确答案:A,D

  • 第9题：

    在Transact-SQL语法中，以下SELECT语句正确的是（）。

    • A、SELECT * FROM student
    • B、SELECT * FROM student WHERE GETDATE（）
    • C、SELECT * FROM student ORDER st_id
    • D、SELECT * FROM student BY St_name

    正确答案:A

  • 第10题：

    The STUDENT_GRADES table has these columns: STUDENT_ID NUMBER(12) SEMESTER_END DATE GPA NUMBER(4,3) Which statement finds the highest grade point average (GPA) per semester?（）

    • A、SELECT MAX(gpa) FROM student_grades WHERE gpa IS NOT NULL;
    • B、SELECT (gpa) FROM student_grades GROUP BY semester_end WHERE gpa IS NOT NULL;
    • C、SELECT MAX(gpa) FROM student_grades WHERE gpa IS NOT NULL GROUP BY semester_end;
    • D、SELECT MAX(gpa) GROUP BY semester_end WHERE gpa IS NOT NULL FROM student_grades;
    • E、SELECT MAX(gpa) FROM student_grades GROUP BY semester_end WHERE gpa IS NOT NULL;

    正确答案:C

  • 第11题：

    The STUDENT_GRADES table has these columns: STUDENT_ID NUMBER(12) SEMESTER_END DATE GPA NUMBER(4,3) The registrar requested a report listing the students' grade point averages (GPA) sorted from highest grade point average to lowest. Which statement produces a report that displays the student ID and GPA in the sorted order requested by the registrar?（）

    • A、SELECT student_id, gpa FROM student_grades ORDER BY gpa ASC;
    • B、SELECT student_id, gpa FROM student_grades SORT ORDER BY gpa ASC;
    • C、SELECT student_id, gpa FROM student_grades SORT ORDER BY gpa;
    • D、SELECT student_id, gpa FROM student_grades ORDER BY gpa;
    • E、SELECT student_id, gpa FROM student_grades SORT ORDER BY gpa DESC;
    • F、SELECT student_id, gpa FROM student_grades ORDER BY gpa DESC;

    正确答案:F

  • 第12题：

    列出EMP表中，从事每个工种（JOB）的员工人数（）

    • A、select job from emp;
    • B、select job,count(*) from emp;
    • C、select distinct job,count(*) from emp;
    • D、select job,count(*) from emp group by job;
    • E、select job,sum(empno) from emp group by job;

    正确答案:D

  • 第13题：

    根据SQL标准，下面哪条语句与select min(age) from student等效?()

    A select age from student where age >= min(age)

    B select distinct age from student where age >= all min(age)

    C select distinct a.age from student a where a.age<= any (select distinctb.age from student b)

    D select distinct a.age from student a where a.age<= all (select distinct b.age from student b)


    参考答案D

  • 第14题：

    根据SQL标准，要查询表student中所有年龄age小于所有学生的平均年龄的记录，下面哪条语句适用?()

    A select * from student where age< avg(age)

    B select * from student having age< avg(age)

    C select * from student a where a.age< (select avg(b.age) from student b)

    D select * from student a where (select avg(b.age) from student b ) >= a.age


    参考答案C

  • 第15题：

    若需统计“选课”表中已经选修了课程的学生人数，下面语句正确的是( )。

    A．SELECT COUNT(DISTINCT学生号)FROM选课

    B．SELECT COUNT(学生号)FROM选课

    C．SELECT COUNT(*)FROM选课

    D．SELECT COUNT(DISTINCT*)FROM选课


    正确答案：A
    解析：选项B是统计选修了课程的学生人次数；选项C是统计选课表中的记录数目；选项D为不正确用法：选项A中用DISTINCT表示不允许出现重复的记录。

  • 第16题：

    如下表student中，如何筛选type为包含数学或语文的记录？（）  ID type score： A01数学78； A02语文76； A03英语90； A04数学68； A05英语84。

    • A、select*from student where type=”数学”and type=”语文”
    • B、select*from student where type=”数学”or type=”语文”
    • C、select*from student where type in（”数学”，”语文”）
    • D、select*from student where type in（”数学”､”语文”）

    正确答案:B,C

  • 第17题：

    The STUDENT_GRADES table has these columns: STUDENT_ID NUMBER(12) SEMESTER_END DATE GPA NUMBER(4,3) The registrar has asked for a report on the average grade point average (GPA) for students enrolled during semesters that end in the year 2000. Which statement accomplish this? （）

    • A、SELECT AVERAGE(gpa) FROM student_grades WHERE semester _ end > '01-JAN-2000' and semester end <31-DEC-2000';
    • B、SELECT COUNT(gpa) FROM student grades WHERE semester _ end > '01-JAN-2000' and semester end <31-DEC-2000';
    • C、SELECT MIN(gpa) FROM student grades WHERE semester _ end > '01-JAN-2000' and semester end <31-DEC-2000';
    • D、SELECT AVG(gpa) FROM student_grades WHERE semester _ end BETWEEN '01-JAN-2000' and '31-DEC-2000';
    • E、SELECT SUM(gpa) FROM student grades WHERE semester _ end > '01-JAN-2000' and semester end <31-DEC-2000';
    • F、SELECT MEDIAN(gpa) FROM student_grades WHERE semester _ end > '01-JAN-2000' and semester end <31-DEC-2000';

    正确答案:D

  • 第18题：

    下列SQL语句中，能够完成求某列最大值的是（）。

    • A、SELECT AVG（Age） FROM Student
    • B、SELECT MAX（Age） FROM Student
    • C、SELECT MIN（Age） FROM Student
    • D、SELECT COUNT（*） FROM Student

    正确答案:B

  • 第19题：

    数据库中有一张表名称为Student，有列Number，Name，Age，IDCard，Sex。主键为Number。要求查询所有男同学信息，下列哪个SQL语句是正确的？（）

    • A、Select* From Student Where Sex=’男’
    • B、Select* From Student Where Number NotIn（Select Number From Student Where Sex<>=’男’）
    • C、Select* From Student Where NumberIn（Select Numbe rFrom Student Where Sex=’男’）
    • D、Select* From Student Where Sex<>’男’

    正确答案:A,B

  • 第20题：

    查询student表中的所有非空email信息，以下语句正确的是（）

    • A、Select email from student where email!=null
    • B、Select email from student where emailnotisnull
    • C、Select email from student where email<>null
    • D、Select email from student where emailisnotnull

    正确答案:D

  • 第21题：

    Examine the description of the EMPLOYEES table: EMP_ID NUMBER(4) NOT NULL LAST_NAME VARCHAR2(30) NOT NULL FIRST_NAME VARCHAR2(30) DEPT_ID NUMBER(2) Which statement produces the number of different departments that have employees with last name Smith?（）

    • A、SELECT COUNT(*) FROM employees WHERE last_name='Smith';
    • B、SELECT COUNT(dept_id) FROM employees WHERE last_name='Smith';
    • C、SELECT DISTINCT(COUNT(dept_id)) FROM employees WHERE last_name='Smith';
    • D、SELECT COUNT(DISTINCT dept_id) FROM employees WHERE last_name='Smith';
    • E、SELECT UNIQUE(dept_id) FROM employees WHERE last_name='Smith';

    正确答案:D

  • 第22题：

    The STUDENT_GRADES table has these columns: STUDENT_ID NUMBER(12) SEMESTER_END DATE GPA NUMBER(4,3) Which statement finds the highest grade point average (GPA) per semester?（）

    • A、SELECT MAX (gpa) FROM student _ grades WHERE gpa IS NOT NULL;
    • B、SELECT (gpa) FROM student _ grades GROUP BY semester_end WHERE gpa IS NOT NULL;
    • C、SELECT MAX (gpa) FROM student _ grades WHERE gpa IS NOT NULL GROUP BY semester_end;
    • D、SELECT MAX (gpa) GROUP BY semester_end WHERE gpa IS NOT NULL FROM student _ grades;
    • E、SELECT MAX (gpa) FROM student _ grades GROUP BY semester_end WHERE gpa IS NOT NULL;

    正确答案:C

  • 第23题：

    The STUDENT_GRADES table has these columns: STUDENT_ID NUMBER(12) SEMESTER_END DATE GPA NUMBER(4,3) The register has requested a report listing the students' grade point averages (GPA), sorted from highest grade point average to lowest within each semester, starting from the earliest date. Which statement accomplishes this?（）

    • A、SELECT student_id, semester_end, gpa FROM student_grades ORDER BY semester_end DESC, gpa DESC;
    • B、SELECT student_id, semester_end, gpa FROM student_grades ORDER BY semester _end, ASC,gpa ASC;
    • C、SELECT student_id, semester_end, gpa FROM student_grades ORDER BY semester _end, gpa DESC;
    • D、SELECT student_id, semester_end, gpa FROM student_grades ORDER BY gpa DESC,semester_end DESC;
    • E、SELECT student_id, semester_end, gpa FROM student_grades

    正确答案:C

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